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單項(xiàng)選擇題

The boiler is fired （） the demand for steam exceeds that available from exhaust gas heating.

A.whenever
B.however
C.wherever
D.whether

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單項(xiàng)選擇題

Gear pumps are （） because they discharge a near constant amount of liquid regardless of pressure.

A.negative displacement type
B.turbine type
C.positive displacement type
D.mixed-flow type

單項(xiàng)選擇題

Keep compartment （） as the gas given off can be dangerous.

A.well ventilated
B.well clean
C.in good order
D.more room

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