His shoes are muddy. He        be working in an office all day.

A．mustn ’t

B．can’t

C．needn’t

D．maybe

扣件式钢管脚手架在搭设封顶时，其外排立杆顶端，平屋顶必须超过女墙顶（）。并绑扎两道护身栏，一道挡脚板，立挂安全网。

A.0.7m

B.0.8m

C.0.9m

D.1.0m