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问题 选择题

若关于x的一元二次方程（x-a）2=4，有一个根为1，则a的值是（　　）

A．3

B．1

C．-1

D．-1或3

答案

把x=1代入方程（x-a）2=4，

可得（1-a）2=4，

解得a=-1或3；

故选D．

单项选择题

You are a project manager who was just assigned to take over a project from another project manager who is leaving the company. The old project manager tells you that the project is on schedule only because he has had to constantly push the team to perform. What is the FIRST thing you should do as the new project manager

A) Check risk status.
B) Check cost performance.
C) Determine a management strategy.
D) Tell the team your objectives.
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单项选择题

关于“噬菌体侵染细菌的实验”的叙述，正确的是（）

A.分别用含有放射性同位素35S和放射性同位素32P的培养基培养噬菌体

B.分别用35S和32P标记的噬菌体侵染未被标记的大肠杆菌，进行长时间的保温培养

C.用35S标记噬菌体的侵染实验中，沉淀物存在少量放射性可能是搅拌不充分所致

D.32P、35S标记的噬菌体侵染实验分别说明DNA是遗传物质、蛋白质不是遗传物质
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