If the machine makes a mistake -- ____ r
题型:选择题
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
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