In the combustion chamber, the part whose surface is exposed to the highest temperature is the （）.

A.ff overheat is found, the engine must be stopped for inspection
B.Much heat of the crankcase door indicates that the bearing is overheated
C.If bearing clearance is too large, knocking will be heard in the crankcase
D.If bearing clearance is too large or too small, the white metal may be melted

A.Because the piston is exposed to very high temperature, it must be cooled
B.The lower the piston cooling temperature is, the better it is
C.Both water and lube oil can be used as coolant
D.One of the piston cooling methods is vibration cooling, with better effect

A.crankshaft
B.piston
C.connecting rod
D.bearing