题目

There was a lot of fun at yesterday's party. You ________ (come), but why didn't you? 答案：should have come 句意：昨天的聚会很有趣。你本应该来，为什么没来呀？should have done sth.表示本应该做某事而实际上没做。组成染色体和染色质的主要物质是A. 蛋白质和DNA B. DNA和RNAC. 蛋白质和RNA D. DNA和脂质