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【简答题】
分析电路时为方便起见，把电流的参考方向规定为由电压参考极性的正极指向负极，称为（）参考方向。
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举一反三
【单选题】is the hardest substance ever known of all materials.
A.
Diamond
B.
carbon steel
C.
High-speed steel
D.
Cubic boron nitride
【单选题】请根据短文的内容，回答题。 Maglev Trains (1) A few countries are using powerful electromagnets to develop high-speed trains, calledmaglev trains. Maglev is short for magnetic levitation, which means that these tra...
A.
The main components of the maglev train system
B.
High-speed maglev due to zero friction
C.
The working principle of the maglev train
D.
Differences between polarity and magnetic field
E.
Comparison of maglev trains with traditional ones
F.
Maglev with a powerful motor
【简答题】Below is a list of alloy steels:AISI52100(GCr15);T91;Superalloy;High-speed steel; 9% nickel medium-alloy steel;AISI 9260;AISI 80;AISI 321 stainless steel.Select from this list the one alloy this is ...
【简答题】Vincent Van Gogh was a painting of later _______ (impress) .
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