问题 选择题

如图是人的前臂工作示意图,下列说法正确的是(  )

A.人的前臂在工作时相当是一个等臂杠杆

B.人的前臂在工作时相当是一个省力杠杆

C.人的前臂在工作时相当是一个费力杠杆

D.人的前臂在工作时既可以省力又可以省功

答案

人的前臂可视为杠杆,当曲肘将物体向上举起,动力臂小于阻力臂,是费力杠杆,它可以省距离.

故选C.

选择题
阅读理解

Tom and his best friend Rob were out of school for the summer. They had been swimming, gone to the movies, played video games, and even built a castle out of some old cardboard boxes. But today they were so bored. “At least we would have something to do.” Tom thought for a while and suggested, “Let’s make some popcorn and lemonade and sell it outside.”

The boys went to the kitchen and asked Tom’s mom if she would help them make some lemonade while they popped the popcorn. Tom’s mom got the lemons from the refrigerator and also a small amount of sugar. She mixed up the lemonade while the boys started popping the popcorn.

Tom and Rob got a small table from the garage and set it up near the sidewalk. They made a red sign telling everyone that popcorn and lemonade was for sale. The boys sat for about ten minutes before they got their first sale. Mrs. Jenkins, one of their neighbors, was walking her dog. “It’s so hot today.” “I sure can use a drink,” she said. Soon the boys were busy handing out popcorn to Mr. Baker. He was walking down the street sending the mail. “I need a break,” he said. “Walking all over the neighborhood gave me an appetite.”

The boys had only three popcorn bags left and enough lemonade for three more cups. “Wow, I didn’t think the popcorn and lemonade would sell that fast. We made six dollars,” said Tom. “If we get bored again before school starts, we can try selling more lemonade with cookies(饼干) next time,” laughed Rob.

小题1:What did Tom suggest?

A.Swimming with their friends.

B.Buying some sugar and cookies.

C.Making some popcorn and lemonade.

D.Going to the movies and playing games.小题2:Where did Tom and Rob set up the table?

A.Near the sidewalk.

B.In the kitchen.

C.At the supermarket.

D.Outside the school.小题3:What did Tom and Rob learn from this experience?

A.People might prefer to buy things on sale.

B.They could do something new to have fun.

C.Mr. Baker liked sending mails very much.

D.Mrs. Jenkins needed help to walk the dog.