Why hasn't he come? ______on time, we will have to put off the trip.
A. If he doesn't come
B. If he won't come
C. If he shouldn't come
D. If he hadn't come
第7题
下列哪项不是血浆蛋白的主要功能
A.运输物质
B.参与机体的免疫
C.缓冲pH值
D.维持血浆晶体渗透压
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