单项选择题
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．have been challenged C．may be challenged D．are challenging
单项选择题 （）nothing more to discuss, the CEO got to his feet, said goodbye and left the meeting room.
单项选择题 It seems oil（）from this pipe for some time. We'll have to take machine apart to put it right.
单项选择题 （）he was a regular customer, the boss allowed 10% discount off the prices of the goods.
