No one the building without the permission of the policeman.
A. is leaving
B. will be leaving
C. has left
D. is to leave
网友回答
A. is leaving
B. will be leaving
C. has left
(答案→)D. is to leave
解析：考查将来时的表达法。本句中的be to do sth表示计划的事情；或者表示注定要做某事；也可以表示命令做某事，相当于have to, must，should;句意；没有警察的允许没有人可以进入大楼。表示的是一种命令。故D正确。