问题
选择题
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
答案
答案：C
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。