问题 单项选择题

如图4-55所示,大三角块A置于光滑水平面上,小三角块B置于大三角块A的斜面上,整个系统无摩擦。系统初始静止,在重力作用下B块沿斜面向下运动,A块也会发生水平运动。直至B块落地之前,下述说法正确的是()。

A.在运动过程中,水平地面的约束力是为常量

B.A,B块之间的约束力沿斜面法线与A,B的运动方向都不垂直,因而此处的约束力作功之和不为零

C.B块的机械能守恒

D.在t时刻,小三角块水平方向的动量值较大

答案

参考答案:A

单项选择题
阅读理解

Dear editor,

Mary is my friend and she is a very good-hearted girl. She’s always the first to help out others. But her habits make me mad sometimes and she just won’t change her ways. For most situations, that’s just fine with me, as I know it’s what make her who she is. However, sometimes it’s just so hard for me to bear her behavior. She has recently got a cellphone, but she often borrows mine to make calls. My phone has a chain with it. She always tries to open it like her own phone. I usually open it for her, but not always, as sometimes I’m driving my car, so she needs to get it out of my purse and open it herself.

This weekend we were at a party in a faraway village. She borrowed my cellphone. As it was cold outside, I let her take it outside without opening it. Now it’s broken because she didn’t open it properly. I wouldn’t be so mad, but over the weekend she also borrowed my car and never offered to pay for the gas, which made me very angry. She should have offered to pay for the gas. As I have mentioned, she’s the type to help out others when and where she can. Perhaps because of that, she thinks others should also do the same for her. Sometimes I just think she is very childish. I don’t want to hurt her, but I do want to let her know that not everyone can accept that. What should I do to let her know that?

Yours,

Lily

小题1:What is Lily’s purpose in writing this letter?

A.to advise us to be careful when making friends.

B.To tell others what kind of person Mary is.

C.To tell Mary what she thinks of her.

D.To ask for advice from an editor.小题2:We can learn from Paragraph 1 that _____.

A.Mary doesn’t have a cellphone

B.Mary doesn’t have any good habits

C.Lily is sometimes not pleased with Mary’s behavior

D.Lily has asked Mary to change her ways.小题3:What happened at the weekend party?

A.Mary lost Lily’s chain.

B.Mary left before the party was over.

C.Lily’s cellphone was broken.

D.Lily had a quarrel with Mary.小题4:What kind of person is Mary?

A.Friendly and beautiful.

B.Kind and careful.

C.Careful and childish.

D.Warm-hearted but childish