pwd-26-Q3

pinkcutie

Q32 to 35

   In 1975 Chinese survey teams

remeasured Mount Everest, the highest

of the Himalayan mountains. Like the

Line  British in 1852, they used the age-old

(5) technique of “carrying in” sea level:

   surveyors marched inland from the

   coast for thousands of miles, stopping

   at increments of as little as a few feet

   to measure their elevation, and mark-

(10) ing each increment with two poles.

To measure the difference in elevation

between poles, surveyors used an

optical level—a telescope on a level

base—placed halfway between the

(15) poles. They sighted each pole, read-

ing off measurements that were then

used to calculate the change in eleva-

tion over each increment. In sight of

the peaks the used theodolites—

(20) telescopes for measuring vertical and

   horizontal angles—to determine the

   elevation of the summit.

The Chinese, however, made

efforts to correct for the errors that

(25) had plagued the British. One source

of error is refraction, the bending of

light beams as they pass through air

layers of different temperature and

pressure. Because light traveling.

(30) down from a summit passes through

many such layers, a surveyor could

sight a mirage rather than the peak

itself. To reduce refraction errors, the

Chinese team carried in sea level to

(35) within five to twelve miles of Everest’s

    summit, decreasing the amount of air

that light passed through on its way to

their theodolites. The Chinese also

launched weather balloons near their

(40) theodolites to measure atmospheric

temperature and pressure changes

to better estimate refraction errors.

Another hurdle is the peak’s shape.

When surveyors sight the summit.

(45) there is a risk they might not all

measure the same point. In 1975

the Chinese installed the first survey

beacon on Everest, a red reflector

visible through a theodolite for ten

(50) miles, as a reference point. One

more source of error is the uneven-

ness of sea level. The British

assumed that carrying in sea level

would extend an imaginary line from

(55) the shore along Earth’s curve to a

point beneath the Himalaya. In

reality, sea level varies according

to the irregular interior of the planet.

The Chinese used a gravity meter to

correct for local deviations in sea level.

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Q32

It can be inferred from the passage that

refraction would be most likely to cause

errors in measurements of a mountain’s

elevation under which of the following

conditions?

A.     When there are local variations in sea

level

B.     When light passes through humid air

C.    When theodolites are used relatively far

from the mountain peak.

D.    When weather balloons indicate low air

temperature and pressure.

E.     When sea level has been carried in to

Within five to twelve miles of the summit.

我觉得是c，可是答案是D,求教...