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【单选题】
关于宿主控制的限制修饰现象的本质,下列描述 不太恰当的是A.
由作用于同一 DNA 序列的两种酶构成
B.
这一系统中的核酸酶都是Ⅱ类限制性内切核酸酶
C.
这一系统中的修饰酶主要是通过甲基化作用对 DNA 进行修饰
D.
不同的宿主系统具有不同的限制 - 修饰系统
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举一反三
【单选题】听力原文：W: You look worried, David. Anything wrong with you? M: Oh, it's nothing really. W: Arc you sure? Would you like to talk about it? M: Well, to be honest, it's.., it's my mother. She... she.., how...
A.
Because his father has suddenly had a heart attack.
B.
Because his wife has been behaving strangely.
C.
Bemuse his mother is still unhappy about his father's death.
D.
Because his daughter is all alone in a very big apartment by the sea.
【单选题】What he had said about the incident and done with it _________ our trouble.
A.
added up to
B.
added to
C.
added up
D.
were added to
【简答题】A．He wants the doctor to look at his mouth. B．He wants the doctor to look at his eyes. C．He wants the doctor to look at his face. D．He wants the doctor to look at his teeth.
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