在“噬菌体侵染细菌”的实验中，若放射性同位素主要分布在离心管

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问题选择题

在“噬菌体侵染细菌”的实验中，若放射性同位素主要分布在离心管的沉淀物中，则获得用于侵染细菌的噬菌体的方法是 [ ]

A．用含³⁵S的培养基直接培养噬菌体

B．用含³²P的培养基直接培养噬菌体

C．先用含³⁵S的培养基培养细菌，再用该细菌培养噬菌体

D．先用含³²P的培养基培养细菌，再用该细菌培养噬菌体

答案

答案：D

填空题

如图所示的小实验中，当水倒入时可以观察到硬币变________（选“浅”或“深”），这是由于光发生了________（选“折射”或“反射”）的缘故。

补全对话，情景问答

根据对话情景，在画线处填上适当的单词，使对话完整通顺。

A: Oh, dear, it is cold today, isn't it?

B: Oh, do you think it's 1 ? I think it's quite warm today.

A: That's because you're wearing 2 clothes.

B: Do you like this time of year? It's spring now. I think spring is the best time of year.

A: Do you? Why?

B: 3 winter is over! What about you? Which is your 4 season?

A: Oh, I love summer best. I enjoy swimming.

B: I like swimming, too. But I like 5 a kite best. It's a pleasure to fly a kite with my friends on

a fine day in spring.