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关于PCR的说法不正确的是： [ ]

A．PCR是体外复制DNA的技术

B．PCR过程中需要一个模板DNA、两个引物分子、大量脱氧核苷酸原料

C．Taq酶是一种热稳定的DNA聚合酶

D．PCR利用的是DNA双链复制原理

答案

答案：B

阅读理解
阅读理解。
     What is your wish for the New Year? The following is some children's ideas.
John: I wish to be a better boy to Mum and listen to her more. I also want to get better grades in school.
Kate: My wish is to change my school as there's too much to study in this school.
Ann: I wish I could spend more time with Mum. She should stop working at the bank and take up a job
at our neighborhood toy shop.
Peter: I wish someone would find a way to help me walk with my only leg, so I can take part in activities 
         and sports that I'm unable to do now.
Mary: I wish that I could save all my money, so I could buy presents for my mother, father and big sister
         on their birthdays.
Bob: I wish for good health though I'm badly ill. I want to finish high school and take an IT course after.
Mark: I wish I could get more money to fix our house. There is a big hole in the wall and big mice run
         inside the room.
1. How many children have mentioned their parents in the passage?
A. All.
B. Four.
C. Three.
D. None.
2. Who is badly ill among the children?
A. Kate.
B. Peter.
C. Mary.
D. Bob.
3. What's Mark's wish?
A. To get better grades.
B. To change his-school.
C. To buy some presents.
D. To fix their house.
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选择题
如图所示，两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R，导轨电阻可忽略不计；MN为放在ab和cd上的一导体杆，与ab垂直，其电阻也为R；整个装置处于匀强磁场中，磁感应强度的大小为B，磁场方向垂直于导轨所在平面（指向图中纸面内）；现对MN施力使它沿导轨方向以速度v（如图）做匀速运动；令U表示MN两端电压的大小，则（　　）

A．U=vBl，流过固定电阻R的感应电流由b到d

B．U=vBl，流过固定电阻R的感应电流由d到b

C．U=vBl，流过固定电阻R的感应电流由b到d

D．U=vBl，流过固定电阻R的感应电流由d到b
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