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【单选题】
PCR过程与细胞内的DNA复制过程相比,主要有两点不同,它们是 1PCR过程需要的引物是人工合成的;2PCR过程不需要DNA聚合酶;3PCR过程中DNA的不依靠酶,而是通过对反应温度的控制来实现的;4PCR过程中,DNA不需要,直接以DNA为模板进行复制A.
③④
B.
①②
C.
①③
D.
②④
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【单选题】Try your best to run fast, ________ you will fall behind others. [ ]
A.
and
B.
but
C.
so
D.
or
【单选题】. As Christmas draws near, they feel more and more uneasy with their stored money ____.
A.
to be run out
B.
to run out of
C.
being run out
D.
running out
【单选题】Don't run in the hallways, or you may _____ somebody. [ ]
A.
knock into
B.
knock at
C.
fall into
D.
fall down
【单选题】It is said that the transport company will soon run ______ petroleum.
A.
over
B.
down
C.
off
D.
out of
【单选题】Beginning from a long run equilibrium in an increasing cost industry, if there is a substantial, permanent fall in demand for industry output:
A.
firms will leave the industry, the quantity produced will fall, and prices will end up lower than their initial long run equilibrium level.
B.
firms will leave the industry, the quantity produced will fall, and prices will end up higher than their initial long run equilibrium level.
C.
firms will leave the industry, the quantity produced will fall, and prices will end up at the same level as their initial long run equilibrium level.
D.
firms will enter the industry, the quantity produced will rise, and prices will end up lower than their initial long run equilibrium level.
【单选题】If oil supplies run out, the man may have to fall back on the horse.(改错题)
A.
run
B.
the man
C.
to fall
D.
on
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