求问prep2012的一道sc：

25. VSC002602


After long years of indifferent reception by the scientific community, Barbara McClintock's subtle work on the genetics of corn has now been acknowledged to be of major importance; her analyses show that movable elements control the action of genes and thus cause mutations.
A. Barbara McClintock's subtle work on the genetics of corn has now been acknowledged to be of major importance


B. Barbara McClintock's subtle work on the genetics of corn has now been acknowledged as being major


C. it has now been acknowledged that Barbara McClintock's subtle work on the genetics of corn is major in importance


D. there is now acknowledgment of Barbara McClintock's subtle work on the genetics of corn as of major importance


E. the importance of Barbara McClintock's subtle work on the genetics of corn has now been acknowledged to be major


答案是A，我想知道为什么不能选C呢？里面的it可以看成是placeholder吗？

我想问下这一题的B为什么不太好？求解答

I just attack choice C in meaning （macro-level）


you should know that non-underlined portion is quite important in this question


the existence of semicolon is used to connect two closely related things


even given that choice C can indeed has  it as placeholder


a fact has now been acknowledged has not thing to do with what BM‘s study shows


that problem is non-existent in choice A


the two parts are closely related