Please help me with this one taken from 800GMATset:

As literary criticism grows more complex, students majoring in specialized areas like
those of post-colonialism and Marxist discourse have been becoming increasingly
successful at finding positions in the faculties of top universities.
A. majoring in specialized areas like those of post-colonialism and Marxist discourse
have been becoming increasingly
B. who major in such specialized areas as post-colonialism and Marxist discourse are
becoming more and more
C. who majored in specialized areas such as those of post-colonialism and Marxist
discourse are being increasingly
D. who major in specialized areas like those of post-colonialism and Marxist
discourse have been becoming more and more
E. having majored in such specialized areas as post-colonialism and Marxist
discourse are being increasingly

OA is: B

Please explain ...