问题 单项选择题 A1/A2型题

DNA的解链温度指的是()

A.A达到最大值时的温度

B.A达到最大值的50%时的温度

C.DNA开始解链时所需要的温度

D.DNA完全解链时所需要的温度

E.A达到最大值的50%时的温度

答案

参考答案:B

解析:DNA的变性从开始解链到完全解链,是在一个相当窄的温度范围内完成的,在这一范围内,紫外光吸收值达到最大值的50%时温度称为DNA的解链温度。

阅读理解

Joe Brown had a shop. He sold(卖) meat in his shop . One Thursday a woman came into his shop at five to one . “I’m sorry I’m late,” she said. “I need some more meat for my dinner tonight.” Joe had only one piece of meat in his shop. He took it out of the fridge and said, “This is$6.50.”  “That piece is too small.” the woman said, “haven’t you for anything bigger?” Joe went into the room behind his shop, put the piece of meat into the fridge, took it out again and closed the door with lots of noise. Then he brought the piece of meat to the woman and said, “This piece of meat is bigger and more expensive. It’s $8.75.” “Good,” the woman said with a smile,“give me both of them.”

(   )1.Joe Brown was_______________.

A. a waiter                            B. a runner       

C. an actor                            D. a shopkeeper

(   )2.When did the woman come to Joe’s shop?

A. Early in the morning.         B. Early in the afternoon.

C. Late in the morning.          D. At about one o’clock at night.

(   )3.Why didn’t the woman want that piece of meat?

A. Because she had no money.       B. Because it was bad.

C. Because it wasn’t big enough.     D. Because it was too big

(   )4.How many pieces of meat were kept in the fridge?

A. Only one piece of meat.            B. Two pieces of meat.

C. Several pieces of meat.            D. Many pieces of meat.

(   )5. Could Joe give the woman both pieces of meat?

A. Of course not.                          B. Certainly.     

C. He would try his best.                    D. Yes, he could.

选择题