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

答案为“C”。句意为“尽管牛顿很伟大，他的许多思想今天受到挑战，并正在为现代科学所修正。”