下述哪项化验对诊断有帮助

A．大便常规
B．AFP
C．CEA
D．大便细菌培养
E．血小板计数，凝血酶时间

Kort nozzles are installed around the propellers of some vessels to（）.

A.Increase the thrust of the propeller

B.Protect the propeller from striking sawyers

C.Prevent the propeller from striking barges towed on the ship

D.Prevent the propeller from touching bottom in low water