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【判断题】
选用粗粒度及较软的砂轮可提高砂轮的切削性能,同时砂轮又不易被磨屑阻塞,有利于防止磨削烧伤的发生。A.
正确
B.
错误
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举一反三
【单选题】We generally take the convention of safety of life at sea adopted in 1974 as a completely new convention, the reason is _____.
A.
it included the amendments agreed up until that date
B.
it included none of the amendments agreed up until that date
C.
it required two thirds of the Parties’ acceptance for a amendment to enter into force
D.
it included a tacit acceptance procedure
【简答题】证明折射光束的方向是等光程方向．即证明图1-14中 L(A 1 B 1 D 1 )=L(A 2 B 2 D 2 )．
【简答题】如图，已知∠１＝∠２，∠A=∠D,证明：∠E=∠C
【简答题】设D=[0，1]×[0，1]，证明函数 在D上部可积。
【简答题】证明 若Dξ=0，则{x=Eξ}=1．