请教一道没人问过的好像

lijiaxuan810823

 Studying the fruit fly, a household nuisance but a time-honored experimental
            subject, has enabled the secrets of how embryos develop to begin to be
            unraveled by scientists.

A.      Studying the fruit fly, a household nuisance but a time-honored experimental
        subject, has enabled the secrets of how embryos develop to begin to be unraveled by scientists.

B.       By the study of the fruit fly, a household nuisance and also a time-honored experimental subject, it was possible for the secrets of how
        embryos develop to begin to be unraveled by scientists.

C.      By studying a household nuisance but a time-honored experimental subject, the fruit fly enabled scientists to begin to unravel the secrets of how
        embryos develop.

D.      By studying the fruit fly, a household nuisance and also a time-honored
        experimental subject, the secrets of how embryos develop are beginning to be unraveled by scientists.

E.       The study of the fruit fly, a household nuisance but a time-honored experimental subject, has enabled scientists to begin to unravel the secrets of how embryos develop.

answer is d，but i chose e 

jessie0317

应该E吧

D错误也太多了 主语不妥， by studying和by scientists也重复