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【单选题】
在火焰原子吸收光谱中 , 测定元素铝宜选用( )火焰。A.
空气 - 乙炔富燃
B.
空气 - 乙炔贫燃
C.
N 2 O-C 2 H 4 富燃
D.
N 2 O-C 2 H 4 贫燃
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【单选题】艾滋病病毒属于RNA病毒，具有逆转录酶，如果它决定某性状的一段RNA含碱基A为19%、C为26%、G为32%，则通过逆转录过程形成的双链DNA中碱基A占 [ ]
A.
19%
B.
21%
C.
23%
D.
42%
【简答题】Please fill in the blanks according to what you hear. 1) __________ is a big problem. Many places on 2) __________ are not clean. There is 3) __________ on the land and in the water. The air is 4) ___...
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【简答题】rewrite the following passage as required: Mom and Dad would get up an hour before they woke up our children and start a fire. Our bed room was very cold on many winter nights. When we were called to...
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【简答题】pollution 1(无字幕).mp4 1)__________ is a big problem. Many places on 2) __________ are not clean. There is 3) __________ on the land and in the water. The air is 4) __________, too. People, cars, 5) ___...
【单选题】艾滋病病毒属于RNA病毒，具有逆转录酶，如果它的一段RNA含碱基A23%、C19%、G31%，则通过逆转录过程形成的双链DNA中碱基A的比例是 [ ]
A.
23%
B.
25%
C.
31%
D.
50%
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