问题

If the machine makes a mistake — ____ rarely happens — it gives a warning in the form of a red light.

A:that
B:which
C:as
D:what

正确答案是：

同类题型

Wh_______ go out.

You have to ____smoking. It isn’t good for your health.

It’s too hot. Would you mind _______ the door—_______, please do it now.

Would you like to come to the party — _________.

eople ________ not have plans yet for New Year’sEve, but others know exactly what they will be doing.