区队必须在作业规程中规定过断层至少（）棚的工字钢棚、背木、坑木、网片、防倒棚卡具、超前管缝等备用支护材料。

A、30

B、10

C、20

        go straight On to university why not get some work experience first?

A．Rather than

B．More than

C．As well as

D．Along with