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單項選擇題

High-speed rotation in a centrifugal purifier can produce a force （） the force of gravity.

A.many thousand times larger than
B.the same as
C.many thousand times smaller
D.none of the above

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The separation of impurities and water from （） is essential for good combustion of diesel engines.

A.lube oil
B.fuel oil
C.turbine oil
D.grease

單項選擇題

Which of the following may hardness of the boiler water cause?（）
(1) scale formation
(2) tube failure
(3) corrosion

A.（1）and（2）
B.（1）and（3）
C.（2）and（3）
D.（1），（2）and（3）

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