游客一旦走失后，导游员怎么处理?
参考答案：
了解情况，迅速寻找;争取有关部门的协助;努力做好善后工作;写出事故处理报告;
当发售免费出站票时必须由（）到场确认。
A.客运值班员及以上人员
B.值班站长
C.站长
D.行车值班员
Jenny ______ with him at that time, for I was having dinner with her in my home.
A．can’t have been
B．mustn’t have been
C．must be
D．may be
