單項(xiàng)選擇題

（）, the motion would continue indefinitely once it had started.

A.Were there loss of energy by friction
B.Since there be loss of energy by friction
C.Were there no loss of energy by friction
D.Should be no loss of energy by friction

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單項(xiàng)選擇題

（） the bodies are, （） the friction will be.

A.The smoother；the greater
B.Smoother；less
C.The rougher；the greater
D.rougher；greater

單項(xiàng)選擇題

Convection is the principal means （） temperature is equilibrated in liquids and gases.

A.in which
B.on which
C.by which
D.from which