题目

—Is this your ________ visit to my hometown,Zunyi?—No.I’ve been here for many times. A.one              B.the first            C.first 答案：C解析: 略下列烯烃中存在顺反异构体的是A. 丙烯 B. 2-丁烯 C. 1-戊烯 D. 2-甲基-2-丁烯