补色是加色混合后成（）的两个互补色光。
A.黑色或灰色
B.白色或灰色
C.黑色
D.白色
参考答案：B
将生地黄制成熟地黄，天南星制成胆南星，其目的在于（）。
A.提高疗效
B.改变药物性能
C.便于服用
D.改变药物作用部位
E.消除或降低毒性
You______ her in her office last Friday; she's been out of town for two weeks.
A．needn't have seen
B．must have seen
C．might have seen
D．can't have seen
