---Did you get a ticket?

---Yes. Otherwise I____ the concert last night.

A．didn’t attend

B．wouldn’t attend

C．hadn’t attended

D．couldn’t have attended

土方开挖如不能立即进行下一道工序，要预留( )cm厚覆盖土层，待基础施工时再挖去。

A．15～30
B．10～25
C．20～35
D．25～40