煤是属于（）。

A.变质岩

B.沉积岩

C.岩浆岩

D.火成岩

If a hydraulic pump on a winch accidentally stops while hoisting,the load will stay suspended because（）.

A.a check valve will close that prevents reverse circulation

B.a centrifugal counterweight counteracts the force of gravity

C.the electric pump motor cut out

D.the control lever will move to the stop position