问题 问答题 简答题

什么是金属的弹性变形?

答案

参考答案:

金属在外力作用下,其内部必将产生应力。此应力迫使原子离开原来的平衡位置,从而改变了原子间的距离,是金属发生变形,并引起原子位能的增高。但是处于高位能的原子具有返回低位能平衡位置的倾向,这种除去外力后,金属完全恢复原状的变形称为弹性变形。

阅读理解

It was the old lady’s eightieth birthday. She was sure Myra wouldn’t forget her mother’s birthday, even if she was busy. After all, eighty was a special birthday. Perhaps Myra might come. Even if Myra did not come, she would send a present. The old lady was sure of that. Two spots of colour brightened her cheeks. She was excited like a child.

Mrs. Morrison had brought a card and a bunch of flowers when she came to do the breakfast. Mrs. Grant downstairs had made a cake. Johnnie, the little boy next door, was now up with her with a packet of sweets.

“I guess you’ll get lots and lots of presents, ” he said. “I did last week when I was six.”

What would she like? A pair of slippers, perhaps. A blue new cardigan(羊毛衫). Or a table lamp. Or a little clock, with clear black numbers. So many lovely things.

She stood by the window, watching. The postman turned round the corner on his bicycle. Her heart beat fast. Johnnie had seen him too and ran to the gate.

“Granny, granny, ” Johnnie returned. “I’ve got your post!”

He gave her four envelopes. Three were from old friends. The fourth was in Myra’s writing.

“No parcel(包裹), Johnnie?”

“No, granny.”

Almost reluctantly, she tore the fourth envelope open. Folded in the card was a check. Written on the card was a message: Happy Birthday—Buy yourself something nice with the check, Myra and Harold.

The six-figure check fell to the floor like a bird with a broken wing. Slowly the old lady bent to pick it up. Her present, her lovely present. With trembling fingers she tore it into little bits.

小题1:As can be inferred from the passage, _______.

A.the old lady lived alone in a flat away from her daughter

B.the friends sent the old lady many lovely presents by post

C.Myra was stopped by her husband from seeing her mother

D.the neighbours cared little about the old lady in daily life小题2:The old lady expected her daughter most __________.

A.to send her a present.

B.to send her a check.

C.to come back home to celebrate her birthday.

D.not to return home.小题3:The old lady felt _______ when she saw no parcel came with her daughter’s card.

A.excited

B.happy

C.disappointed

D.impatient小题4:Which of the following might serve as the best title for the passage?

A.The Present

B.The Check

C.The Birthday

D.The Daughter小题5:The reason why the old lady tore the check into small pieces was that _______.

A.she was sure her daughter would come, not the check

B.she didn’t notice there were six figures on the check

C.she didn’t think the check was large enough for a present

D.she would prefer a present with love from her daughter

单项选择题