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问题 选择题

汽车的质量为M，以速率v沿半径为R的拱形桥面行驶，若欲使汽车过桥的中心时对桥面的压力正好为零，汽车的速度应为（　　）

A．

g
R

B．

gR

C．

R
g

D．gR

答案

汽车对桥面压力正好为零，有：mg=m

v2
R
，解得；v=
gR
．故B正确，A、C、D错误．

故选：B．

阅读理解

Some children are afraid to go to the dentist (牙医), but not me. I'm a boy of 8 and I have a funny dentist. His name is Dr. Smileyface. I don't think that's his real (真实的) name. But when the children go to see him, he tells his name to all of them.

He has a cool waiting room.  It has computer games and a big toy box. Dr. Smileyface always wears funny hats. Sometimes he paints his face. He asks funny questions like "Are you married（结婚）?" and "Do you eat flowers to make your breath (呼吸)  smell so sweet?" That makes me laugh. One time, he tells me this joke (玩笑）, "What has lots of teeth but never goes to the dentist? A comb (木梳) ! " When I laugh, he pulls my tooth out. It doesn't hurt at all (一点不疼)! He also tells me how to take care of my teeth in an interesting way. Before I leave (离开), he always gives me a surprise (惊喜). This time he gives me a toy ship and I like it very much.

小题1:How does the writer(作者) feel when he goes to the dentist?

A．Angry.

B．Afraid.

C．Sad.

D．Happy.小题2:What does Dr. Smileyface tell the writer to do?

A．How to laugh.

B．How to take care of his teeth.

C．To eat flowers.

D．To paint his face.小题3:What does Dr. Smileyface give the writer this time?

A．A toy ship.

B．A toy box.

C．A comb.

D．Flowers.
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单项选择题

（ ）is a collection of data sets, which is so large and complex that it becomes difficult to process using on-hand database management tools or traditional data processing applications.

A. Big data

B. Cluster

C. Parallel computing

D. Data warehouse
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