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
B:which
C:as
D:what
正确答案是：
同类题型
Which is the _________clothes store in town
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n’t need to describe her, I ___ her serveral times.
Cheer up! Everyone may have periods in their liveseverything seems tough.