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單項(xiàng)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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單項(xiàng)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

單項(xiàng)選擇題

All three systems have the ports （） to swirl the incoming air and direct it in the appropriate path.

A.angled
B.rounded
C.being angled
D.being rounded