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

When did the young man save you? —January 1st,2000, the first day of the new century,_______ I can never forget

By this time next yearhe from the college.

ssage is very important, so it is supposed assoon as possible.

now aims to boost domestic demand, and this______ would help the global economy.

Only when________ possible to settle the problem.