18 In cermet, metal plays as the binder of ceramic particles, normally its total amount no more than vol%.（请填数值）

Salt, shells or metals are still used as money in out-of-the-way parts of the world today. Salt may seem rather a strange 【B1】 to use as money, 【B2】 in countries where the food of the people is mainly vegetable, it is often an 【B3】 necessity. Cakes of salt, stamped to show their 【B4】 , were used as money in some countries until recent 【B5】 and cakes of salt 【B6】 buy goods in Borneo and parts of Africa. Sea shells 【B7】 as money at some time 【B8】 another over the greater part of the Old World. These were 【B9】 mainly from the beaches of the Maldives Islands in the Indian Ocean, and were traded to India and China. In Africa, shells were traded right across the 【B10】 from East to West. Metal, valued by weight, 【B11】 coins in many parts of the world. Iron, in lumps, bars or rings, is still used in many countries 【B12】 paper money. It can either be exchanged 【B13】 goods, or made into tools, weapons, or ornaments. The early money of China, apart from shells, was of bronze, 【B14】 in flat, round pieces with a bole in the middle, called "cash". The 【B15】 of these are between three thousand and four thousand years old--older than the earliest coins of the easterr Mediterranean. Nowadays, coins and notes have 【B16】 nearly all the more picturesque 【B17】 of money, and 【B18】 in one or two of the more remote countries people still keep it for future use on ceremonial 【B19】 such as weddings and funerals, examples of 【B20】 money will soon be found only in museums.

【B1】

A．object

B．article

C．substance

D．category

Salt, shells or metals are still used as money in out-of-the-way parts of the world today.

Salt may seem rather a strange (31)____ to use as money, (32)_____ in countries where the food of the people is mainly vegetable, it is often an (33)_____ necessity. Cakes of salt, stamped to show their (34)____, were used as money in some countries until recent (35)_____, and cakes of salt (36)____ buy goods in Borneo and parts of Africa.

Sea shells (37)_____ as money at some time(38)____ another over the greater part of the Old World. These were (39)___ mainly from the beaches of the Maldives Islands in the Indian Ocean, and were traded to India and China. In Africa, shells were traded right across the (40)___ from East to West.

Metal, valued by weight, (41)____ coins in many parts of the world. Iron, in lumps, bars or rings, is still used in many countries(42)_____ paper money. It can either be exchanged(43)____ goods, or made into tools, weapons, or ornaments. The early money of China, apart from shells, was of bronze, (44)_____ in flat, round pieces with a hole in the middle, called "cash". The (45)_____ of these are between three thousand and four thousand years old - older than the earliest coins of the eastern Mediterranean.

Nowadays, coins and notes have (46)____ nearly all the more picturesque (47)____ of money, and (48)____ in one or two of the more remote countries people still keep it for future use on ceremonial (49)____ such as weddings and funerals, examples of (50)____ money will soon be found only in museums.

(31) A. object B. article C. substance D. category

(32) A. but B. and C. so D. even

(33) A. abstract B. advantageous C. abundant D. absolute

(34) A. weight B. value C. role D. size

(35) A. times B. events C. situations D. conditions

(36) A. even B. also C. still D. never

(37) A. had been used B. are used C. would be used D. would have been used

(38) A. and B. but C. yet D. or

(39) A. collected B. produced C. grown D. raised

(40) A. city B. district C. communib D. continent

As the shortage of certain metals approaches, others must be found to take their ________.

A) share

B) place

C) role

D) shape

As the shortage of certain metals approaches, others must be found to take their ______

A．share

B．role

C．place

D．shape

听力原文： Aristotle, the Greek philosopher, summed up the four chief qualities of money some 2,000 years ago. It must be lasting and easy to recognize, to divide, and to carry about. In other words it must be, durable, distinct, divisible and portable. When we think of money today, we picture it either as round, flat pieces of metal which we call coins, or as printed paper notes. But there are still parts of the world today where coins and notes are of no use. They will buy nothing, and a traveler might starve if he had none of the particular local money to exchange for food.

Salt may seem rather a strange substance to use as money, but in countries where the food of the people is mainly vegetable, it is often an absolute necessity. Cakes of salt, stamped to show their value, were used as money in Tibet until recent times, and cakes of salt will still be used to buy goods in Borneo and parts of Africa.

(37)

A．It should be made of metal.

B．It should be durable, distinct, divisible and portable.

C．It had been 2,000 years old.

D．It should be made of high-quality materials.

There is no difference between the corrosion of metals and the deterioration of thermoplastics in terms ofweight.

What material were the beads made of?

A．Space particles.

B．Precious stones.

C．Plastic.

D．Metal.

Transportation in the U.S.

Railroads are paths of parallel metal rails that allow a wheeled vehicle to move more easily by reducing friction. Iron mils were first used in the early 1800s to guide horse-drawn wagons. After the invention of the steam locomotive (机车) in 1804, steam engines replaced horses as the primary means of power. Modem locomotives commonly use electric motors or diesel (柴油机) engines and pull long trains of passenger or freight (货物) ears. The benefits of rail transportation in both speed and carrying capacity made it superior to other methods of transportation in the 1800s. In the United States and Canada, with their vast expanses of territory, the railroad became a major means of cross-country transportation. In many countries, rail continues to be the main mode of passenger travel. In Europe and Japan, major cities axe connected by high-speed passenger trains, such as the French TGV (Train Grande Vitesse) and the Japanese Shinkansen (新干线) trains, popularly known as bullet trains (高速火车). The Shinkansen train can reach speeds of 300 km/h (186 mph). Railroads have had a profound impact on civilization. Most importantly, the efficiency and speed of mil travel allow a nation's population, industry, and agriculture to be established throughout that nation's territory, even in previously remote areas. Rail transportation has also played a significant role in urban transportation systems.

Motor vehicles make up a broad class of self-propelled (机动式的) land-transportation devices that generally use internal-combustion engines (内燃机) and gasoline or diesel fuel for power. Most motor vehicles are designed to travel on roads, but specialized vehicles with more solid construction are used for off-road travel over irregular ground. Motor vehicles range from motorcycles and automobiles for personal use to trucks, which can transport large amounts of cargo, and buses, which can carry many passengers. The first self-propelled vehicle was powered by steam. French engineer Nicholas-Joseph Cugnot built a steam-propelled vehicle in 1769. Between 1860 and 1890, innovations in steam-engine technology led to more steam-powered vehicles, primarily in France. At the beginning of the 20th century, gasoline powered automobiles began to emerge as the dominant form. of motor vehicle. Automobiles and other motor vehicles grew especially popular in the United States. From a relatively modest number in 1900, the number of motor vehicles in the United States reached 458,500 by 1910 and 6.2 million by 1918. At the end of the 20th century, over 130 million automobiles, 69 million light trucks, and 1.2 million heavy trucks were in use in the United States, being driven an estimated 4.5 trillion km (2.8 trillion mi) per year. The heavy truck, which first came into mass production just prior to World War Ⅰ (1914-1918), has become a major means of moving freight. It is a major competitor with railroads for freight business. The bus was developed in response to the apparent popularity of tiding in motor vehicles. In many nations buses are a major form. of urban and intercity passenger transportation. The motorcycle is one of the most abundant forms of individual urban transportation in the world today. The growth of motorcycle or motorbike use has been especially large in Asian cities, where motorcycles provide a means of bypassing crowded automobile traffic. One of the few motor vehicles that do not use wheels is the snowmobile, which uses a drive track (made of a belt of robber) and a pair of skis to move through snow. Although used for basic transportation in areas with heavy winter snows, the snowmobile is mostly used as a recreational vehicle. Over 200,000 snowmobiles are sold annually in the United States, Canada, and Europe.

Air travel has revolutionized global transportation by dramatically reducing the time needed to travel great distances. Journeys across nations or oceans that might have taken

A．Y

B．N

C．NG

A panicle is a hollow sphere of a metal oxide.The density of the metal oxide is 2000kg/m³. The hollow portion in the center of the sphere is full of air that has the same density as the surrounding air through which the sphere is falling at its terminal velocity. The outside diameter of the sphere is 10μ and the thickness of its walls is 0.1μ(i.e., the bubble in the center has a diameter of 9.8μ). How fast is it falling?