问题

They were surprised that a child should work out the problem____ they themselves could not

A:once
B:unless
C:while
D:if

正确答案是：

同类题型

When they met ten years later, they talked happily about the people and the things ________ they remembered on the school football team.

“Where is Mother.” “She is in the kitchenShe _______ the housework all morning.”

I can read __________.

inter _______ on, it’s time to buywarm clothes

Everyone was in silence, having nothing to do but _________.