A terrible accident____,however,occur the other day and weA terrible accident _______,however,occur the other day and we witnessed it _______ accident.A.does;byB.did;byC.has to;onD.had to;on我知道答案选B,我想问的是前面一个空为什么不能用had to?（我单独问前面一个空,和后面的by accident 无关）
问题描述：
A terrible accident____,however,occur the other day and we
A terrible accident _______,however,occur the other day and we witnessed it _______ accident.
A.does;by
B.did;by
C.has to;on
D.had to;on
我知道答案选B,我想问的是前面一个空为什么不能用had to?（我单独问前面一个空,和后面的by accident 无关）
答