标出以下所有正确的表述。（）A．转录是以半保留方式获得序列相_爱下问搜题

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问题单项选择题

标出以下所有正确的表述。（）

A．转录是以半保留方式获得序列相同的两条DNA链的过程

B．依赖DNA的DNA聚合酶是多亚基酶，它负责DNA的转录

C．细菌的转录物（mRNA）是多基因的

D．σ因子指导真核生物hnRNA的转录后加工，最后形成mRNA

E．促旋酶在模板链产生缺口，决定转录的起始和终止

答案

参考答案：C

多选题

凸透镜的弯曲表面是个球面，把一个凸透镜压在一块平面玻璃上，让单色光从上方射入，如图所示，从上往下看凸透镜，结果观察到同心的内疏外密的圆环状干涉条纹，称为牛顿环．关于牛顿环，以下说法正确的是（）

A．干涉条纹是凸透镜下表面和平板玻璃上表面的两列反射光叠加而成的

B．干涉条纹不等间距是因为空气膜厚度不是均匀变化的

C．若仅增大入射光的波长，则圆环状干涉条纹的半径变大

D．若仅增大凸透镜的半径，则圆环状干涉条纹变的密集

完形填空

完形填空 (共15小题；每小题1分，共15分)
On a hot summer day in south Florida, a little boy decided to go for a swim in the lake behind his house. In a hurry to dive into the cool water, he ran out of the 36 door, leaving behind his shoes, socks, and shirt as he went.
He 37 into the water, not realizing that as he swam to the middle of the lake, a(n) 38 was swimming toward the 39 . His mother in the house saw the two. Full of 40 , she ran toward the water, screaming at her son as loudly as she could. Hearing her voice, the little boy became 41 and made a U-turn to swim hurriedly to his mother. But it was too late. Just as he reached her, the crocodile 42 him. The mother grabbed her little boy by the 43 just as the crocodile seized his legs.
The crocodile was 44 stronger than the mother; but the mother was much too 45 to pull her son back. A farmer heard the 46 , raced from his truck, took aim and shot the crocodile.
Remarkably, a few weeks later, the little boy 47 . His legs were extremely scarred by the attack of the animal. 48 , on his arms, were deep scratches where his mother’s fingernails dug into his flesh(肉体) in her 49 to hang on to the son she loved.
The newspaper reporter, who 50 the boy after the accident, asked if he would show him his scars（疤痕）: The boy, with obvious 51 , said to the reporter, “But look at my arms. I have great scars on my arms, too. I have them because my mom would not let go.”
You and I can 52 with that little boy. We have scars, too. Not from a crocodile, but the scars of a painful 53 . some of those scars are ugly and have 54 us deep regret. But , some wounds, my friend, are because our relatives have 55 to let go. In the course of your struggle, they have been there holding on to you.

B．interviewed