问题

I had been puzzled over the problem for over an hour without any result, ____ all at once the solution flashed across my mind

A:while
B:when
C:then
D:as

正确答案是：

同类题型

Don’t promise anything ______ you are one hundredpercent sure

unds very much inthe job, but I’m not sure whether he can manage it

I haven’t got the reference book yet, but I’ll have a test on the subject next month. — Don’t worry. You ________ have it by Friday.

What does your sister look like —______________________.

_________ model plane is this—I think it’s Jim’s. Look, his name is on it.