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问题 选择题

若3x-1=32y-3，53y=5x+1，则y-x等于（　　）

A．-5

B．5

C．-3

D．3

答案

∵3x-1=32y-3，53y=5x+1，

∴

x-1=2y-3
3y=x+1
，解得
x=-4
y=-1
，

∴y-x=-1+4=3．

故选D．

选择题

设NA为阿伏加德罗常数的值，下列叙述正确的是（　　）

A．32gO2含有的氧原子数为2NA

B．1L0.1mol•L-1NaCl溶液中所含的Na+数为NA

C．常温常压下，11.2LCl2所含的分子数为0.5NA

D．1molH2O所含有的原子数为NA
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单项选择题

One day while a girl was walking in the woods she found two starving songbirds. She took them home and put them in a small (16) She cared for them and felt great love for them.

Once the (17) and per of the two birds flew from the cage. Therefore, (18) he flew close, she grasped him (19) She felt glad, but suddenly she felt the bird go limp. She opened her hand and (20) in horror at the dead bird.

She noticed the other bird moving back and forth on the edge of the cage. She could feel his great need for (21) She lifted him from the cage and (22) him softly into the air. The bird circled once, twice, three times.

The girl watched delightedly at the bird’ s enjoyment. Her heart was no longer (23) with her loss. Suddenly the bird flew closer and (24) softly on her shoulder. It sang the sweetest melody that she had ever heard.

The fastest way to (25) love is to hold on it too tightly, while the best way to keep love is to give it WINGS!

25().

A.gain 

B.give 

C.lose 

D.show
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