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【单选题】
镁离子在DNA或RNA体外扩增反应的浓度一般为A.
0.3~1mmol/L
B.
0.3~2mmol/L
C.
0.5~1mmol/L
D.
0.5~2mmol/L
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举一反三
【单选题】According to Paragraph 2 ______.
A.
people of higher status are less likely to be stricken with diarrhea
B.
diarrhea is no longer a serious disease in the modem world
C.
diarrhea has been a threat to humanity throughout history
D.
the elderly are more likely attacked by diarrhea than the young
【单选题】下面双代号网络图中,工作 I 的工序关系不正确的( )
A.
工作 D 、 E 、 G 都是紧前工作
B.
工作 H 是平行工作
C.
工作 D 、 E 不是紧前工作
D.
没有紧后工作
【单选题】It can be inferred from Paragraph 2 that human society will become increasingly ______.
A.
worried about life on other planets.
B.
dependent on space tourism.
C.
accustomed to long-distance flights.
D.
associated with space exploration.
【单选题】下列A、B、C、D中有一处是错误的地方,请找出相应的错误字母代码。细胞减数分裂I中期,每条染色体含A2条染色单体,着丝点B分裂,染色体排在C赤道板两侧,此时染色体紧缩至D最短。
A.
B.
C.
D.
D
【单选题】In paragraph 2, why does the author mention that the period for different horseshoe crabs ranges from 22.2 to 25.5 hours?
A.
To illustrate that an animal's internal clock seldom has a 24-hour cycle
B.
To argue that different horseshoe crabs will shift from daytime to nighttime vision at different times
C.
To illustrate the approximate range of the circadian rhythm of all animals
D.
To support the idea that external cues are the only factors affecting an animal's periodic behavior
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