短跑运动员在100m的竞赛中，测得他5s末的速度是8.7m/s，10s末到达终点的速度为10.3m/s，此运动员在这100m中的平均速度的大小是（）

题干

A：9.5m/s

B：10.3m/s

C：9m/s

D：10m/s

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D

Animals are our good friends. Some are active and others are quiet. But do you know anything about the clever animals in the world? Just have a look!

Animals	Interesting facts
	Kelly is an African elephant. Now she is 19 years old. She lives in the zoo. Kelly has produced more than 100 paintings since last year. She has made over $3,500 for the zoo. Newspaper reporters wrote about Kelly, and then people went to buy her pictures.
	Nana is a clever black and white dog in England. He can do many things just like a human. He can walk on two legs and close the door. Also, he is able to get things for his master, such as newspapers and the TV remote control. What's more, he can sleep and use the quilt very well. No games are difficult for him!
	Koko is a 44—year—old chimpanzee. He has lived with human for tens of years and can “talk” to humans with his hands. He can do simple gestures* and that helps people to understand him.