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【单选题】
纯铜焊接时,常常要使用大功率热源,焊前还要采取预热措施的原因是( )。A.
纯铜导热性好、难熔合
B.
防止产生冷裂纹
C.
提高焊接接头的强度
D.
防止锌的蒸发
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举一反三
【单选题】How much money does the man want to exchange?
A.
200 US dollars.
B.
250 US dollars.
C.
300 US dollars.
D.
400 US dollars.
【简答题】试解微分方程2y(y'-1)-xy' 2 =0．
【简答题】试求微分方程2y(y'-1)-xy' 2 =0的奇解．
【单选题】Conerning pair production, which of the following is true?
A.
The threshold energy for pair production is 0.51 MeV.
B.
An electron and a positron are produced.
C.
The energy of the incident photon is equal to the sum of the kinetic energies of the pair of particles.
D.
Annihilation produces 1.02 MeV photons.
E.
A pair of electrons is produced.
【单选题】The turning pair which can have a whole revolution is .
A.
frame
B.
rocker
C.
full turning pair
【单选题】更正错账时，划线更正法的适用范围是
A.
记账凭证上会计科目或记账方向错误，导致账簿记录错误
B.
记账凭证正确，在记账时发生错误，导致账簿记录错误
C.
记账凭证上会计科目或记账方向正确，所记金额大于应记金额，导致账簿记录错误
D.
记账凭证上会计科目或记账方向正确，所记金额小于应记金额，导致账簿记录错误
【简答题】--How do lovers exchange their vows of love on St. Valentine's Day? --Through _____ _____, flowers and _____.
相关题目：
【单选题】The turning pair which can have a whole revolution is .
A.
frame
B.
rocker
C.
full turning pair
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