求英语语法大神!

题目

求英语语法大神!
Great as Newton was, many of his ideas___C___today and are being modified by the work of scientists of our time.
A.are to challenge
B.may be challenged
C.have been challenged
D.are challenging
正确答案是C,我选了D,求解释啊

答案

首先弄明白challenge的意思,动词：挑战,质疑；名词：挑战.在此作动词：质问.
选项分析：BC均为被动,C为现在完成时；AD是主动,A表将来时,B表现在进行时；
many of his ideas：他许多的想法,应该是他的想法被质疑,而不是他的想法质疑,排除AD；
他的许多想法已经被质疑,所以才被改进modified,所以选C