Mr. Zhang has retired already. He       in our school for over thirty years.

A．has worked

B．had worked

C．worked

D．was working

下述关于高处作业中不安全的操作是（）

A.须铺设防滑布

B.作业人员应空硬底鞋

C.作业应戴安全帽

D.作业人员所带工具及用料应放在专用工具袋内