货源供应中，卷烟品牌共分为哪几类？
参考答案：
货源供应中，卷烟品牌共分为三类：紧俏品牌、顺销品牌和新品牌。
高处作业人员应系好安全带，戴好（ ），禁止穿带钉易滑的鞋。
A．安全帽、衣着轻便
B．安全帽、穿好防滑鞋
C．安全帽、架好安全网
— The woman biologist stayed in Africa studying wild animals for 13 years before she returned.
— Oh, dear! She _____ a lot of difficulties! [ ]
A. may go through
B. might go through
C. ought to have gone through
D. must have gone through
