Great as Newton was, many of his ideas 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
网友回答
A. are to challenge
B. may be challenged
(答案→)C. have been challenged
D. are challenging
解析：考查时态。句意“尽管牛顿很伟大，但是他的很多想法在当今已经受到挑战了，正在被当代的科学家进行修改。”发生在过去的事情，对现在造成的影响，用现在完成时。主语是复数，故谓语用原形have。Ideas和challenge是动宾关系，用被动语态。故选C。