Which sentence breaks the unity of the paragraph below written by C.D.B. Bryan?During the later stages of World War II, pilots of advanced fighter...

The sentence which breaks the unity of the paragraph is
the fourth sentence,

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"The Concorde regularly flies at several times
the speed of sound."

All the
other sentences address the topic introduced in the first sentence of the paragraph,
which is the problems encountered when World War II advanced fighter aircraft approached
the speed of sound during high-speed dives. There are three sentences which describe
exactly how these problems were manifest, with the planes being "buffeted and wrenched
about," the controls becoming ineffective and drag setting in, and, in extreme cases,
the planes actually breaking apart and crashing. The last sentence of the paragraph ties
the previously information together, telling what was done to fix the problem introduced
at the beginning of the paragraph and developed
thereafter.

Although the sentence about the Concorde talks
about one part of the topic, the sound barrier, it does not address the main point of
the topic, which is the fighter planes' problems with it. Thus, the sentence about the
Concorde breaks up the unity of the paragraph.