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【多选题】
作为载体应具备以下哪几个特点A.
能够在宿主细胞中保存并大量复制，且对受体细胞无害。
B.
有多种限制性内切酶酶切位点，而且每种酶的酶切位点最好只有一个。
C.
含有复制起点，能够独立复制
D.
有一定的标记基因，便于筛选。
E.
载体DNA分子大小合适，方便进行操作。
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反馈参考答案：
举一反三
【简答题】下列哪一项不能促进胰液的分泌
【简答题】The experienced teacher's ________(explain) to the math problem was clear and to the point.
【单选题】听力原文：M: Ma, I can't finish the math homework, it's too difficult to do. W: You know what to do if there's a problem? Q: What does the woman mean? (19)
A.
The child should know how to solve the math problems.
B.
There won't be any difficulty in the math homework.
C.
She wants to help the child with the math homework.
D.
She wants to find out about the math problems.
【单选题】The math problem is so hard that ______ students can't work it out.
A.
a few
B.
a little
C.
many
D.
few
【单选题】The math problem is so hard that ___students can work it out.
A.
a few
B.
a little
C.
many
D.
few
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