The oil index of main engine should be controlled to prevent it from in heavy weather（）

A.increasing the linear velocity of the exhaust gases
B.changing directions of exhaust gas flow
C.decreasing the temperature of the exhaust gases
D.accelerating the exhaust gas through a reduced size orifice

A.change from heavy fuel oil to diesel oil for mail engine
B.pumping oil bilge water
C.change sea chest form high level one to lower one
D.test emergency generator

A.The cetane number has no affect on injection lag
B.The cetane number is an indication of the fuel’s viscosity
C.Ignition lag is reduced with fuels having a high cetane number
D.The cetane number is of little significance in the combustion