51. It’s high time we_______ something to stop traffic accident．(QE96-43)

        A do              B will do           C. did            D must do

        【答案】C  It is high/about time 引导的句子中要求使用虚拟语气,谓语动词用过去式.句意是“我们该做些什么去停止交通事故.”

        52. If only I _____ how to operate an electronic computer as you do.

        A. had known      B. would know      C. should know     D. knew 

        【答案】D。要是我能像你一样知道如何操作这个电子计算机就好了。固定句型虚拟。

        53. Let’s finish our homework in a few seconds; it’s time we _____. (QE04-11-43)

        played football  B. will play football  C. play football     D. are playing football

        【答案】A 本句考查1t is time that从句(谓语动词用过去时表示虚拟)。

        54. He talks as if he ___ everything in the world. (QE98-27)

        A. knows      B. knew    C. had known    D. would have known

        【答案】B    as if “似乎，好像”引导的从句表虚拟，与现在事实相反，从句中的动词用一般过去时表示虚拟，故选B。句意为：他讲起话来好像知道世界上所有的事一样。

        55. Written applications should be sent to us in case ___ some problems with the electric version. (QE02-59)

        A. there will be    B. there is    C. there be    D. there was

        【答案】C。in case 引导的从句要用虚拟语气，should +原形动词，should 可以省略。