在保证和稳定精煤质量，提高浮选机处理量和降低药剂耗量的前提下，尽量（）是增加可燃体回收率的有效措施。

A.提高精煤灰分

B.降低精煤灰分

C.提高尾矿灰分

D.降低尾矿灰分

When fire pumps are used for other than firefighting service，each pipe connecting the other service (except for branch lines used for deck washing) must have a（）.

A.check valve installed in the line

B.shut off valve at a manifold near the pump

C.quick disconnect union within ten feet of the pump

D.regulator in the line set at 125 psi