Correct Option B
Original sentence:
Unlike birds,
- which are highly sensitive to atmospheric pressure,
-
people have found that paragliding require the use of a variometer since detecting thermal currents are impossible using normal human motion sensitivity.
Sentence meaning:
In contrast similarity of flying, comparison with birds, which are highly sensitive to atmosphere pressure,and can detect thermal currents during their fly, people on other side are unable to measure thermal currents, who are doing paragliding, by normal human motion sensor, to measuring this thermal currents varimotors device is used.
[the use of a variometer crucial for paragliding]
Based on only meaning, A, C, D and E are eliminated,
because the phrase in sentence refer with usage of "
That" as
that paragliding require the use of a variometer, which is wrong,
here "
paragliding" works as a
Noun/Subject,
we need
paragliding as a verb and instrument
varimotors device as
Noun to have intended meaning of the sentence.
Remaining with B and only correct.
(Pronoun It refer to "pressure")