you were ing，I would have stayed at home.
A. If I know
B. Should I know
C. Had I known
D. If I should have known
网友回答
A. If I know
B. Should I know
(答案→)C. Had I known
D. If I should have known
解析：句意：我要是知道你要来，我就呆在家里了。根据I would have stayed at home.可知是和过去相反的虚拟语气，从句用过去完成时，这里可以省略if，将had提前，所以选C。