问题补充：
An awful accident, however, occur the other day.
A. does
B. did
C. has to
D. had to
答案：
A. does
(答案→)B. did
C. has to
D. had to
解析：此题正确答案应选B，句末的the other day意为“前几天”，所以句子应用过去时态，而选项D填进去不合题意，故选B。此句有两个难点：一是句中插有however一词，分散了同学们的注意力；二是所填选项B为许多同学所不熟悉的强调用法。
【标签】动词的强调形式
