求问一道prep的题

yracheld

The ultimate pendulum clock, indeed the ultimate
mechanical clock ofany kind, was invented by a British
engineer, WilliamShortt. The first was installed in the
Royal Observatoryin Edinburgh in 1921. The Shortt
clock had twopendulums, primary and secondary. The
primary pendulumswung freely in a vacuum chamber.
Its only job was tosynchronize the swing of the
secondary pendulum,which was housed in a
neighboring cabinetand drove the time-indicating
mechanism. Every 30seconds the secondary pendulum
sent an electricalsignal to give a nudge to the primary
pendulum. Inreturn, via an elaborate electromechanical
linkage, theprimary pendulum ensured that the
secondary pendulumnever got out of step.

Shortt clocks werestandard provision in astronomical
observatories ofthe 1920s and 1930s, and are credited
with keeping timeto better than two milliseconds in a
day. Many were onrecord as losing or gaining no more
than one second ina year—a stability of one part in
30 million. Thefirst indications of seasonal variations in
the earth'srotation were gleaned by the use of Shortt
clocks.

In 1984 PierreBoucheron carried out a study of a Shortt
clock which hadsurvived in the basement of the United
States NavalObservatory since 1932. After replacing the
electromechanicallinkage with modern optical sensing
equipment, hemeasured the Shortt clock's rate against
the observatory's atomic clocks for a month. He found
that it was stableto 200 microseconds a day over this
period, equivalentto two to three parts in a billion. What
is more, the dataalso revealed that the clock was
responding to theslight tidal distortion of the earth due
to thegravitational pull of the moon and the sun.

In addition tocausing the familiar ocean tides, both the
sun and the moonraise tides in the solid body of the
earth. The effectis to raise and lower the surface of the
earth by about 30centimeters. Since the acceleration due
to gravity dependson distance from the center of the
earth, this slighttidal movement affects the period of
swing of a pendulum.In each case the cycle of the tides
caused the clock togain or lose up to 140 microseconds.


Question 1. The passage most strongly suggests that its author would
agree with which of the following statements about clocks?

A) Before 1921 no one had designed a clock that used
electricity to aid in its timekeeping functions.

B) Atomic clocks depend on the operation of
mechanisms that were invented by William Shortt
and first used in the Shortt clock.

C) No type of clock that keeps time more stably and
accurately than a Shortt clock relies fundamentally on
the operation of a pendulum.

D) Subtle changes in the earth's rotation slightly reduce
the accuracy of all clocks used in observatories after
1921.

E) At least some mechanical clocks that do not have
pendulums are almost identical to Shortt clocks in
their mode of operation

求问这道题 为什么是c不是e？

yracheld

我以为e在原文有原句：“The ultimate pendulum clock, indeed the ultimate mechanical clock ofany kind, was invented by a British engineer, WilliamShortt. " 是不是因为e说"....clock that do not have pendulums"
但是c是从哪儿得出来的呢

megannine

In the second paragraph, we get the following quote about Shortt clocks: Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million.

So we know that these clocks, which rely on the operation of a pendulum, are extraordinarily accurate.

In the next paragraph, in which the Shortt clocks are compared to atomic clocks, we see that the Shortt clocks are nearly as accurate as the atomic clocks, and we also get this: the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun.

So there's almost no difference in accuracy between the Shortt clocks and the atomic clocks (atomic clocks, presumably, being the standard for accuracy) and what difference exists is a function of tidal distortion.

In the last paragraph, we get this line: this slight tidal movement affects the period of swing of a pendulum.

Taken together we know that there's almost nothing more accurate than a Shortt clock; the Shortt clock only falls short of an atomic clock because the tide very slightly distorts its pendulum swing. Because any pendulum clock would suffer from this same distortion, it's reasonable to conclude that clock more accurate than a Shortt clock won't operate via a pendulum. So the answer is C

from https://www.beatthegmat.com/exam-pack-2-rc-pendulum-clock-t293688.html

harvey1123

我这题也选错了，自己看了不少论坛都没法说服自己。还是不太理解Beatthegmat论坛的解释。
我要是强行排出E 只能用atom clock 和mechanical clocks 不能等价?

Quirel

我觉得其实这道题题在考SC....，最主要的是对C选项的理解。
No type of clock（ that keeps time more stably and accurately than a Shortt clock） relies fundamentally on the operation of a pendulum.
这句话真正的主语是 relies on，其语义为：没有其他pendulum clock，比Shortt clock更精准。
所以，C想说的是，在所有的pendulum clock里面，Shortt clock是最准确的。这是符合文章的。

我也选错了，因为当时理解成了：在所有的clock里面，Shortt clock是最准确的。（这个肯定错，因为atomic clocks肯定是最准的）