北京師范大學(xué)考博英語真題（2015年）

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Directions: There are six passages in this part. Each of the passages is followed by five questions or unfinished statements. For each of them there are four choices marked A, B, C and D. Choose the best one and mark your answer on the ANSWER SHEET.

Passage One

The human ear contains the organ for hearing and the organ for balance. Both organs involve fluid-filled channels containing hair cells that produce electrochemical impulses when the hairs are stimulated by moving fluid.

The ear can be divided into three regions: outer, middle, and inner. The outer ear collects sound waves and directs them to the eardrum separating the outer ear from the middle ear. The middle ear conducts sound vibrations through three small bones to the inner ear. The inner ear is a network of channels containing fluid that moves in response to sound or movement.

To perform the function of hearing, the ear converts the energy of pressure waves moving through the air into nerve impulses that the brain perceives as sound. Vibrating objects, such as the vocal cords of a speaking person, create waves in the surrounding air. These waves cause the eardrum to vibrate with the same frequency. The three bones of the middle ear amplify and transmit the vibrations to the oval window, a membrane on the surface of the cochlea, the organ of hearing. Vibrations of the oval window produce pressure waves in the fluid inside the cochlea. Hair cells in the cochlea convert the energy of the vibrating fluid into impulses that travel along the auditory nerve to the brain.

The organ for balance is also located in the inner ear. Sensations related to body position are generated much like sensations of sound. Hair cells in the inner ear respond to changes in head position with respect to gravity and movement. Gravity is always pulling down on the hairs, sending a constant series of impulses to the brain. When the position of the head changes—as when the head bends forward—the force on the hair cells changes its output of nerve impulses. The brain then interprets these changes to determine the head’s new position.

1. What can be inferred about the organs for hearing and balance?

A. Both organs evolved in humans at the same time.

B. Both organs send nerve impulses to the brain.

C. Both organs contain the same amount of fluid.

D. Both organs are located in the ear’s middle region.

2. Hearing involves all of the following EXCEPT ______.

A. motion of the vocal cords so that they vibrate

B. stimulation of hair cells in fluid-filled channels

C. amplification of sound vibrations

D. conversion of wave energy into nerve impulses

3. It can be inferred from Paragraphs 2 and 3 that the cochlea is a part of ______.

A. the outer ear

B. the eardrum

C. the middle ear

D. the inner ear

4. What can be inferred from Paragraph 4 about gravity?

A. Gravity has an essential role in the sense of balance.

B. The ear converts gravity into sound waves in the air.

C. Gravity is a force that originates in the human ear.

D. The organ for hearing is not subject to gravity.

5. In this passage, the author mainly explains ______.

A. the organs of the human ear

B. the function of the hearing

C. the three regions of the ear

D. how the ear organ performs the hearing and balance

Passage Two

The geology of the Earth’s surface is dominated by the particular properties of water. Present on Earth in solid, liquid, and gaseous states, water is exceptionally reactive. It dissolves, transports, and precipitates many chemical compounds and is constantly modifying the face of the Earth.

Evaporated from the oceans, water vapor forms clouds, some of which are transported by wind over the continents. Condensation from the clouds provides the essential agent of continental erosion: rain. Precipitated onto the ground, the water trickles down to form brooks, streams, and rivers, constituting what is called the hydrographic network. This immense polarized network channels the water toward a single receptacle：an ocean. Gravity dominates this entire step in the cycle because water tends to minimize its potential energy by running from high altitudes toward the reference point that is sea level.

The rate at which a molecule of water passes through the cycle is not random but is a measure of the relative size of the various reservoirs. If we define residence time as the average time for a water molecule to pass through one of the three reservoirs—atmosphere, continent, and ocean—we see that the times are very different. A water molecule stays, on an average, eleven days in the atmosphere, one hundred years on a continent and forty thousand years in the ocean. This last figure shows the importance of the ocean as the principal reservoir of the hydrosphere but also the rapidity of water transport on the continents.

A vast chemical separation process takes place during the flow of water over the continents. Soluble ions such as calcium, sodium, potassium, and some magnesium are dissolved and transported. Insoluble ions such as aluminum, iron, and silicon stay where they are and form the thin, fertile skin of soil on which vegetation can grow. Sometimes soils are destroyed and transported mechanically during flooding. The erosion of the continents thus results from two closely linked and interdependent processes, chemical erosion and mechanical erosion. Their respective interactions and efficiency depend on different factors.

6. According to the passage, clouds are primarily formed by water ______.

A. precipitating onto the ground

B. changing from a solid to a liquid state

C. evaporating from the oceans

D. being carried by wind

7. The passage suggests that the purpose of the “hydrographic network” is to ______.

A. determine the size of molecules of water

B. prevent soil erosion caused by flooding

C. move water from the Earth’s surface to the oceans

D. regulate the rate of water flow from streams and rivers

8. What determines the rate at which a molecule of water moves through the cycle, as discussed in the third paragraph?

A. The potential energy contained in water.

B. The effects of atmospheric pressure on chemical compounds.

C. The amounts of rainfall that fall on the continents.

D. The relative size of the water storage areas.

9. All of the following are examples of soluble ions EXCEPT ______.

A. magnesium

B. iron

C. potassium

D. calcium

10. The word “efficiency” in last sentences is closest in meaning to ______.

A. relationship

B. growth

C. influence

D. effectiveness

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