單項選擇題Aluminum pistons have （） coefficient of thermal expansion compared with those of cast iron.

A.higher
B.lower
C.the same
D.none of the above


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1.單項選擇題Although the crankshafts of medium diesel engines appear to be robust, they rely on the support of （） to develop their full strength.

A.the piston rods
B.the crank throws
C.the thrust bearings
D.the main bearings

3.單項選擇題All the rings are slightly rounded on their external top and bottom edges to keep the oil film on the cylinder liner during （） for new piston rings.

A.the running-in period
B.the running process
C.gas exchange process
D.the boiler firing

4.單項選擇題Air cocks, usually positioned at the （） in a circulating system, is used to get rid of the air in the system.

A.bending joint
B.expansion tank
C.weld
D.the highest point

5.單項選擇題After the order “（）” is given, the air system is shut down, the turning gear put in.

A.Finished with Engine
B.Stop the Engine
C.Stand-by Engine
D.Slow-down Engine