Powering the industrial revolution - 英檢

Paragraph 2: The source had long been known but not exploited. Early in the
century, a pump had come into use in which expanding steam raised a piston in
a cylinder, and atmospheric pressure brought it down again when the steam
condensed inside the cylinder to form a vacuum．This “atmospheric engine,”
invented by Thomas Savery and vastly improved by his partner．Thomas
Newcomen, embodied revolutionary principles, but it was so slow and wasteful
of fuel that it could not be employed outside the coal mines for which it had
been designed. In the 1760s, James Watt perfected a separate condenser for
the steam, so that the cylinder did not have to be cooled at every stroke;
then he devised a way to make the piston turn a wheel and thus convert
reciprocating (back and forth) motion into rotary motion. He thereby
transformed an inefficient pump of limited use into a steam engine of a
thousand uses. The final step came when steam was introduced into the
cylinder to drive the piston backward as well as forward thereby increasing
the speed of the engine and cutting its fuel consumption.

5. According to paragraph 2，the atmospheric engine was slow because
○it had been designed to be used in coal mines
○the cylinder had to cool between each stroke
○it made use of expanding steam to raise the piston in its cylinder
○it could be operated only when a large supply of fuel was available

Ans:(B)

想請問C為什麼不對 如果我只看 the atmospheric engine的前一句“a pump had come
into use in which expanding steam raised a piston in a cylinder”看起來C也沒有
問題，而且這題的答案是在蠻後面"so that the cylinder did not have to be cooled
at every stroke"，這個答案也沒有很明確的說明是造成slow的原因

好苦惱阿~~~~

麻煩各位解答一下了

謝謝!!


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