When did his father ______ yesterday?[ ]
A: arrive
B: reach
C: get to
D: got to
答案:A
下列物质中存在顺反异构体的是( )
A.2-氯丙烯
B.丙烯
C.2-丁烯
D.1-丁烯
提高通用冒口补缩效率的措施是什么?