采取下述哪种措施可以提高机械效率    (    ) A.有用功一定,

采取下述哪种措施可以提高机械效率    (    )

A.有用功一定,增大总功    B.总功一定,增大额外功

C.有用功一定,减小总功    D.额外功一定,减小有用功

答案

C

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