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【单选题】
关于功的概念有以下几种说法: (1) 保守力做正功时,系统内相应的势能增加.(2) 质点运动闭合路径,保守力对质点做的功为零.(3) 作用力和反作用力大小相等、方向相反,所以两者所做的功的代数和必然为零.在上述说法中
A.
(1)、(2)是正确的
B.
(2)、(3)是正确的
C.
只有(2)是正确的
D.
只有(3)是正确的
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举一反三
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同种色调和
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类似色调和
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【单选题】By saying 'Stevie soon graduated from toy instruments to real instruments', the author means that________
A.
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A.
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B.
Stevie began to study in a real instruments school
C.
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A.
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B.
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