我在山东大学英语系学习了4年。此处表明现在已经毕业，以前在山大学习过4年。故用一般过去时。
418．--- Would you have called her up had it been possible? --- Yes, but I busy doing my homework. A．was B．am C．had been D．would be A考查动词时态。句意：过去我正在做功课。
419. Unexpected difficulties ____in the course of their experiment.
A. arises B. were arising C. arose D. were arisen C考查动词时态。根据in the course of their experiment可知用一般过去时。
420．--- Do you think we should accept that offer?
--- Yes, we should, for we such bad luck up till now, and time out. A．have had; is running B．had; is running C．have; has been run D．have had; has been run
A考查动词时态。第一空由up till now可知用现在完成时；第二空用进行时表将来时。 421．By the time he realizes he into a trap, it’ll be too late for him to do
anything about it. A．walks B．walked C．has walked D．had walked C考查动词时态。句意：直到他意识到他已经走进圈套时，他再做什么都晚了。
422．This is the first time we a film in the cinema together as a family. A．see B．had seen C．saw D．have seen D考查动词时态。此处考查This is the first time句型，其后用现在完成时。 423．I along the street looking for a place to park when the accident . A．went; was occurring B．went; occurred C．was going; occurred D．was going; has occurred
C考查动词时态。句意：当我正在沿着大街走以寻找停车的地方时，这时意外事故发生了。
424．--- It was really very kind of you to give me a lift home. --- Oh, don’t mention it. I past your house anyway. A．was coming B．will come C．had come D．have come
A考查动词时态。语境：---很感谢你把我带回家。---不用谢。不管怎么我也要路过你家。此
处用进行时表将来时。 425.— How about buying Sam a mobile phone? After all, he isn’t a boy any more. — I think it necessary, for we sometimes want to make sure if he _______ home for dinner.
A. will come B. comes C. has come 答案：A. 此句为宾语从句，根据句意可知是一般将来时。
D. would come
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