- He _______ (go) to the store every weekend. A. goes B. went C. is going D. will go
答案：A. goes 解释：这句话表示一个习惯性的动作，通常用一般现在时来表示。因此，正确的选项是 “goes”。
- She _______ (not study) for her exam last night. A. doesn’t B. didn’t C. doesn’t have D. hasn’t
答案：B. didn’t 解释：这句话描述的是过去的一个动作，即昨晚她没有复习考试。因此，正确的选项是 “didn’t”。
- By the time you _______ (arrive) at the airport, the flight _______ (already leave). A. will arrive; has already left B. arrive; has already left C. will arrive; will already leave D. arrive; has already left
答案：D. arrive; has already left 解释：这是一个关于将来完成时的句子。第一个空格应该用一般现在时，因为 “by the time” 引导的从句通常用一般现在时来表示将来。第二个空格应该用现在完成时，因为动作发生在过去的某个时间点之后，并且对现在有影响。因此，正确的选项是 “arrive; has already left”。
- If I _______ (know) that, I would have helped you. A. knew B. know C. had known D. will know
答案：C. had known 解释：这是一个虚拟语气的句子，用来表示与过去事实相反的情况。在这种情况下，主句用 “would have + 过去分词”，从句用 “had + 过去分词”。因此，正确的选项是 “had known”。
- They _______ (finish) their homework by now if they had started earlier. A. would finish B. would have finished C. will finish D. finished
答案：B. would have finished 解释：这是一个虚拟语气的句子，表示与过去事实相反的情况。在这种情况下，主句用 “would have + 过去分词”，因此正确的选项是 “would have finished”。