_______time,they would certainly come and help us.
问题描述：
_______time,they would certainly come and help us.
A.If had they
B.If they had
C.Had they
D.Both B and C
Explain it.
答
选B.
如果if放在句首,主谓位置不能调换；用虚拟语气时如果倒装,只把助动词、系动词和情态动词放到句首而不把实义动词放在句首,由于C选项中的had是实义动词（拥有）,所以应选B.