Which of the following may take place if the clearance of the main bearings are excessive?（）

A.starting air pressure too high
B.correct timing of starting air valves
C.three of the six starting valves stuck
D.the turning gear disengaged

A.too low starting air pressure
B.main start valve closed
C.neither A nor B
D.A and B

A.The process begins after TDC
B.The process ends before TDC
C.When the piston is near to the TDC the fuel injection ends
D.None of the above is true