As the information technology field matures, programmers
specializing in particular niches like those of web design and application development have been becoming increasingly marketable to firms that currently outsource projects to boutique contractors.
Whole sentence needs to be in simple present tense. No other tenses are preferred.
(A) specializing in particular niches like those of web design and application development
have been becoming increasingly-
Incorrect for having used present perfect tense(B) who specialize in such particular niches as web design and application development are becoming more and more(C) who
specialized in particular niches such as those of web design and application development
are being increasingly-
Incorrect for having used past tense and improper usage of being and increasingly(D) who specialize in particular niches
like those ofweb design and application development
have been becoming more and more-
Incorrect for having used present perfect tense and like for indicating examples instead of such as(E)
having specialized in such particular niches as web design and application development are
being increasingly-
Incorrect for having used present perfect tense and being error as in C.