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【单选题】
1968年.在几篇新闻报道中描述了一个惊人的发现,有2%到4%的精神病患者的性染色体组成为XYY。XYY综合征患者有暴力倾向,有反社会行为,有人称多出的这条Y染色体为“犯罪染色体”。下列关于XYY综合征的叙述正确的是( )A.
患者为男性.是由母亲减数分裂产生异常卵细胞所致
B.
患者为男性.是由父亲减数分裂产生异常精子所致
C.
患者为女性。是由母亲减数分裂产生异常卵细胞所致
D.
患者为女性。是由父亲减数分裂产生异常精子所致
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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】High-speed steel is also ___________________(know) as self-hardening steel.
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