皮皮学，免费搜题
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搜题
【单选题】
睾丸绒毛膜上皮癌的声像图特点是A.
内部回声不均匀，为中强回声
B.
内部回声不均匀，为中等回声
C.
内部回声均匀，为中强回声
D.
内部回声均匀，为中等回声
E.
内部回声均匀，为强回声
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参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】I wanted to have him ______ the job, but she had it _____ already.
A.
do, done
B.
does, doing
C.
to do, doing
D.
to do, done
【简答题】重组载体疫苗(recombinant vector vaccine)(名词解释)
【简答题】微机控制点火系中最佳点火提前角由 、 、 组成。
【单选题】I wanted to have him _____ the job, but she had it _____ instead.
A.
do/done
B.
does/doing
C.
to do/doing
【多选题】How is recombinant DNA cloned in bacteria?
A.
To clone a particular fragment of DNA, it is first inserted into a plasmid vector. To insert a piece of DNA into a plasmid vector, the purified plasmid DNA is opened up by a restriction enzyme that cleaves it at a single site, and the DNA fragment to be cloned is then spliced into that site using DNA ligase. This recombinant DNA molecule is now ready to be introduced into a bacterium, where it will be copied and amplified.
B.
The resulting recombinant plasmid DNA is then introduced into a bacterium by transformation. These bacteria are then suspended in a nutrient-rich broth and allowed to proliferate.
C.
In 24 hours, the engineered cells will produce hundreds of millions of copies of the plasmid, along with the DNA fragment it contains. The bacteria can then be split open (lysed) and the plasmid DNA purified from the rest of the cell contents, including the large bacterial chromosome.
D.
The DNA fragment can be readily recovered by cutting it out of the plasmid DNA with the same restriction enzyme that was used to insert it, and then separating it from the plasmid DNA by gel electrophoresis. Together, these steps allow the amplification and purification of any segment of DNA from the genome of any organism.
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