A, and D - Eliminated because of
SV agreement -
theses isA, and E - Eliminated because use of
Whereas - is a conjuction used in contrast or comparison with the fact, most of the cases prefered to be used between the two joining sentence, and rarely starting of the sentence followed to Noun.
Approximately,
Generally, and
Usually - all 3 are Adverb, maintain parallelism, which is absent in & will eliminate option - C, and E
With use of
While as a conjunction between two clause, maintained adverb parallelism, and intended meaning -
B is Good option.(A)
Whereas a typical Master's
thesis is approximately one hundred pages long, Ph.D
theses is usually - eliminated
(B) A typical Master's
thesis is approximately one hundred pages long, while a Ph.D
thesis is generally
(C) A typical Master's
thesis is approximately one hundred pages long, so a Ph.D
thesis is usually - eliminated
(D) While typical Master's
theses is approximately one hundred pages long, Ph.D
theses is generally - eliminated
(E)
Whereas a typical Master's
thesis is approximately one hundred pages long, a Ph.D
thesis is - eliminated