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【简答题】
肺炎双球菌转化实验中, S 型菌的部分 DNA 片段进入 R 型菌内,并整合到 R 型菌的 DNA 分子上,使 R 型菌转化为 S 型菌。下列叙述正确的是 A .在进入 R 型菌的 DNA 片段上,有 RNA 聚合酶的结合位点 B . R 型菌转化成 S 型菌的过程中, R 型菌发生了染色体变异 C . R 型菌转化成 S 型菌前后的 DNA 中,嘌呤所占比例发生了改变 D . S 型菌的翻译过程中, mRNA 上可同时结合多个核糖体共同合成一条肽链
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【单选题】They were ahead during the first half of the match, but they ________ in the last five minutes．
A.
were beating
B.
beat
C.
were beaten
D.
had been beaten
【简答题】We were ahead during the first half of the match， but we ______ in the last ten minutes. (A)lost (B) have lost (C) were losing (D) had lost
【单选题】During the first half of the seventeenth century, when the nations of Europe were quarreling over who owned the New World, the Dutch and the Swedes founded competing villages ten miles apart on the De...
A.
Convenience for traffic.
B.
The Delaware River.
C.
The investment of Irenee DuPont.
D.
The textiles mills.
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