According to the passage, which of the following statements best describes the relationshi

true?

A．These temperature gradients tend in most cases to be impossible to describe mathematically.

B．The lower the contrast between the extremes of the gradient, the lower the resulting velocity of the jet stream.

C．Jet streams are responsible for most of the north-south transfer of heat between the equator and the poles.

D．The temperature gradient tends, on a non-negligible level, to augment the effects of the earth's rotation.

E．The gradient typically refers to differences in jet stream velocity at various longitudinal positions around the globe.

Detailed knowledge of each of the jet streams of the earth's hemispheres-

its location, altitude and strength-is critical to modern-day weather

forecasting, as well as to more specific applications such as the routing of

Line aircraft. By way of definition, a jet in fluid dynamics is simply a core of fluid

(5) moving at a higher velocity than the surrounding fluid, and although

complicated to describe mathematically, the jet streams in the atmosphere are a

straightforward, natural result of the meridional (equator-to-pole) temperature

gradient in the earth' s atmosphere. Analogous flows exist on other planets with

substantial atmospheres having similar temperature gradients.

(10) The temperature gradient derives from the differential solar heating of the

spherical surface of a planet: the surface is generally warmest at the equator

and grows progressively cooler as one moves poleward. The centrifugal effects

of the earth's rotation, often called the Coriolis force, deflect the north-south

transport of heat from the equator to the poles into the predominantly east-west

(15) motion of the jet stream. The relative strength, or velocity, of the jet stream is

proportional to the intensity of this thermal gradient. During the winter

months, when the equator-to-pole temperature disparity is at its greatest, the

jet stream reaches its maximum velocity, while during the summer months,

when the temperature gradient between the equator and the pole is considerably

(20) less, the jet stream reaches its minimum velocity.

The jet stream does not maintain a straight, zonal flow from west to east

but rather takes on a more serpentine look, often with dramatic dips to the

south or rises to the north. There are two major reasons for these nonzonal

motions: the temperature gradient between the equator and the poles and the

(25) presence of land masses on the earth's surface. The meridional temperature

gradient between the equator and poles that gives rise to the jet stream also

produces secondary atmospheric circulations, or eddies which, referred to by

meteorologists as baroclinic waves, have a complex interaction with the jet

stream, one that is intriguingly two-sided. The eddies modify the distribution of

(30) temperature and kinetic energy within the atmosphere, a process that has a

pronounced effect on the location and movement of the jet stream, which itself

interacts with these waves, acting not only as a transport or steering

mechanism but transferring momentum and energy back to the waves.

The presence of land masses on the earth's otherwise watery surface also

(35) modifies the distribution of temperature, because continents heat and cool at a

dramatically slower rate than do the oceans. The topography of the land also

influences the jet stream's location-mountain ranges and plains on large

continents, for example, significantly imbalance the distribution of atmospheric

temperature, narrowing the jet stream. And since the jet stream is a thermally

(40) driven phenomenon, the more complicated the three-dimensional temperature

structure of the earth's atmosphere, the more "wand

A．interpret data

B．explain research methodology

C．evaluate a conclusion

D．suggest a new technique

E．describe a phenomenon

ing cases?

A．A small population with low consumption rates, considered globally

B．A large population with high consumption rates, considered nationally

C．A large population with low consumption rates, considered globally

D．A small population with high consumption rates, considered nationally

E．A small population with high consumption rates, considered globally

tion effects physiological energy requirements tend to be

A．entirely superfluous

B．globally consistent

C．not wholly explanatory

D．supremely crucial

E．unfortunately complicated

development to be

A．unoriginal

B．inaccurate

C．offensive

D．obscure

E．speculative

Witkins rightly argues that population may be deemed a valid sustainable

development indicator—that sustainability can only be implemented by limiting

population below the carrying capacity of the Earth. This thesis works relatively

Line well when one presupposes that global per capita consumption is homogenous,

(5) and that the global ecosystem can perform. with uniform. effectiveness the tasks

of supplying resources and assimilating wastes, but in reality population effects

vary widely due to vast regional differences in ecosystem characteristics. While

large populations exert considerable stress on their ecosystems, small

populations with high rates of consumption can eclipse the effect of larger

(10) populations operating at lower rates of consumption. Per capita consumption of

energy may exponentially exceed the physiological energy requirements of

humans, requiring that both population and consumption be taken into account.

Witkins thus ignores the corollary that the impact of population tends to be more

significant on a national level than that of consumption adjusted population, but

(15) on a global level, the opposite obtains.

The passage supplies information that would answer which of the following questions?

A．What accounts for the difference in rates of consumption in certain countries?

B．What is the numerical factor by which per capita energy consumption exceeds physiological energy requirements?

C．Which countries tend to have more sensitive ecosystems, those with small or large populations?

D．What factor in calculating sustainability has Witkins neglected to consider in his theory of global development?

E．What evidence is there for the notion that higher rates of consumption can be more important than population rates in calculating the impact of development?

based solely on turbulence patterns would be

A．revolutionary

B．unreliable

C．outdated

D．derivative

E．inconsequential

ollision in turbulence for which of the following reasons?

A．The "sling effect" remains unproven and requires experimental corroboration.

B．The degree to which droplets collide is the only reliable method of assessing air flow.

C．The degree of turbulence may help forecast the formation of large-size droplets that precipitate rain.

D．Such factors as warm and cold fronts and individual cloud formations could not be performed otherwise.

E．The laws which govern the formation of concentration heterogeneities still need to be discerned.

small droplets of equal size to form. in cloud cores. Ⅱ. Causes different concentrations of rain droplets to form. in different places. Ⅲ. Speeds up the rate by which large droplets appear.

A．Ⅰ only

B．Ⅱ only

C．Ⅰ and Ⅱ only

D．Ⅱ and Ⅲ only

E．Ⅰ,Ⅱ, and Ⅲ

SECTION 3

Directions: Each passage in this group is followed by questions based on its content. After reading a passage, choose the best answer to each question. Answer all questions following a passage on the basis of what is stated or implied in the passage.

Air turbulence can substantially accelerate the appearance of large droplets

triggering rain by presenting a new mechanism, the "sling effect", which

increases collisions of droplets that have become detached from the airflow.

Line First, vapor condensation in cloud cores produces small droplets resembling one

(5) another in size, which then expand to raindrop size by coalescing under the

effects of air turbulence—a force thought to cause collisions of similar-sized

droplets whose radii exceed a few micrometers. Then, turbulent vortices act as

small centrifuges that spin heavy droplets out, creating concentration

heterogeneities and jets of droplets, both of which increase the mean collision

(10) rate, which in turn accelerates rain initiation.

One can conclude that rain prediction requires a quantitative description of

droplet collision in turbulence, a mechanism which helps meteorologists to

forecast rainfall, but detailed understanding of the phenomenon entails

consideration of such factors as warm and cold fronts stretching over hundreds

(15) of miles, individual clouds perhaps a mile or so across, and even, as the

mechanism illustrates, tiny eddies perhaps a few centimeters or so in size.

The primary purpose of the passage is to

A．explain and resolve a controversy among meteorologists

B．present and describe a recently discovered phenomenon

C．suggest and prove a theory on the cause of a phenomenon

D．describe and confirm research findings under question

E．discuss and evaluate the soundness of certain experimental observations