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【单选题】
关于A260和A280的测定,下列描述错误的是( )A.
蛋白质在280nm波长处有吸收高峰，是因为绝大多数蛋白都含有色氨酸和酪氨酸这两种氨基酸，这两者在280nm处有最大吸收峰；
B.
测定DNA样品的A260/A280，1.8
C.
测定RNA样品的A260/A280，比值>2.0，表明RNA样品可能有降解；
D.
核酸在260nm波长处有强烈的吸收，是由碱基的共轭双键所决定。
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【单选题】对下图所示零件的尺寸标注,哪种说法是正确的?
A.
螺纹M6必须标注在粗实线圆上
B.
直径5.3的孔标注正确
C.
直径为10的孔上必须用小写字母“h”
D.
孔10H7的标注是正确的
【简答题】如下图所示零件视图,不正确表达局部视图的是()A. B. C.
【单选题】______was regarded as America s poet laureate and invited to read his poem at the inauguration of President kennedy.
A.
T. S. Eliot
B.
E. E. Cummings
C.
Robert Frost
D.
Ezra Pound
【单选题】Thomas Jefferson was inaugurated (举行就职典礼) on March 4, 1801. He was the first President to take the oath of office (宣誓就职) in the nation's permanent capital, Washington, D.C. Although Washington was a n...
A.
The Presidential Palace was not located there.
B.
It contained many old buildings in 1801.
C.
It was not the first capital of the United States.
D.
Thomas Jefferson was a newcomer there in 1801.
【单选题】Recognize the Figures of Speech in the Following Sentences and Appreciate how they are used. 1 ) Let both sides explore what problems unite us instead of belaboring those problems which divide us. ( J...
A.
contrast
B.
couplet
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