在酮糖存在下单独测定醛糖的方法为

A、正交

B、斜交

C、单向曲线

D、反向曲线

A、腐败

B、酸败

C、发酵

D、都不是

A、浅孔一般指深度不大于3～5m，孔径为30～46mm的炮孔。

B、开采缓倾斜薄矿体时，炮孔布置一般采用水平布置。

C、中硬以下选用风动式凿岩机

D、水平孔落矿受采场空顶面积或矿体厚度限制

A、模压法

B、刀具冲裁法

C、剪刀剪裁法

D、粘合法

A、中内龙骨

B、旁内龙骨

C、舭肘板

D、肋板

Nobody really knows how big Lagos is. What'sindisputable is that it's growing very quickly. Between now and 2050, the urban population ofAfrica could triple. Yet cities in sub-Saharan Africa are not getting richer the way cities in therest of the world have. Most urban Africans live in slums （贫民窟）; migrants are often notmuch better off than they were in the countryside. Why? The immediate problem is poverty. Most of Africa is urbanising at a lower level of income thanother regions of the world did. That means there's little money around for investment thatwould make cities liveable and more productive. Without upgrades and new capacity, bridges, roads and power systems are unable to cope with expanding populations. With the exceptionof South Africa, the only light rail metro system in sub-Saharan Africa is in Addis Ababa, Ethiopia. Traffic jam leads to expense and unpredictability, things that keep investors away. In other parts of the world, increasing agricultural productivity and industrialisation wenttogether. More productive farmers meant there was a surplus that could feed cities; in turn, that created a pool of labour for factories. But African cities are different. They are too oftenbuilt around consuming natural resources. Government is concentrated in capitals, so is themoney. Most urban Africans work for a small minority of the rich, who tend to be involved ineither cronyish （有裙带关系的） businesses or politics. Since African agriculture is still broadlyunproductive, food is imported, consuming a portion of revenue. So what can be done? Though African countries are poor, not all African cities are. In Lagos, foreign oil workers can pay as much as 65,000 dollars per year in rent for a modest apartmentin a safe part of town. If that income were better taxed, it might provide the revenue for betterinfrastructure. If city leaders were more accountable to their residents, they might favourprojects designed to help them more. Yet even as new roads are built, new people arrive. Whena city's population grows by 5% a year, it is difficult to keep up. 46.What do we learn from the passage about cities in sub-Saharan Africa? A.They have more slums than other cities in the world. B.They are growing fast without becoming richer. C.They are as modernised as many cities elsewhere. D.They attract migrants who want to be better off. 47.What does the author imply about urbanisation in other parts of the world? A.It benefited from the contribution of immigrants. B.It started when people's income was relatively high. C.It benefited from the accelerated rise in productivity. D.It started with the improvement of peopled livelihood. 48.Why is sub-Saharan Africa unappealing to investors? A.It lacks adequate transport facilities. B.The living expenses there are too high. C.It is on the whole too densely populated. D.The local governments are corrupted. 49.In what way does the author say African cities are different? A.They have attracted huge numbers of farm labourers. B.They still rely heavily on agricultural productivity. C.They have developed at the expense of nature. D.They depend far more on foreign investment. 50.What might be a solution to the problems facing African cities? A.Lowering of apartment rent. B.Better education for residents. C.More rational overall planning. D.A more responsible government.

A、A

B、B

C、C

D、D

A、1, 5, 7

B、3, 5, 7

C、1, 3, 7

D、1, 3, 5

A、生物鉴别法

B、生化鉴别法

C、化学鉴别法

D、色谱鉴别法

A、驱动装置

B、滚珠丝杠

C、导轨

D、床身