MX展现框架中$extend表示（）A、继承B、重构C、覆盖D、扩展

June 5 is World Environment Day.This makes us pay more attention to our environment and the need to protect it.

When Wang Baoxuan,a Beijing high school boy,finishes his exercise books,he does not throw them away.He puts them in the big box in the corner of his classroom.Other students do so.Then the exercise books are sold to a paper-factory in Beijing.The paper is collected and used again by students and teachers in the school.At the same time,the money made from selling the paper goes towards schools in Inner Mongolia  for planting trees and grass.During spring time,the sandstorms often attack here.

Wang’s school is one of the schools in the capital that take part in the “green promise”environmental protection activity.So far,nearly 210,000 students have taken part in the activity,collecting more than 174 kilograms of waste paper.

“There are some environment problems in the city,such as sandstorms.We should do our duty and encourage others to do so as well.”Said Wang.

Vice-premier Zeng Peiyan has written a letter to the teachers and students to encourage them to go on taking part in the environmental protection.

小题1:What do Wang Baoxuan and his schoolmates do with the waste exercise books?

A．Throw them away

B．Collect and sell them

C．Cut them into pieces

D．Give them to the students in Inner Mongolia小题2:What is the money from selling the paper used for?

A．Buying new exercise books

B．Helping poor students

C．Planting trees and grass

D．Being their pocket money小题3:What can we infer(推断)from the third paragraph?

A．Many years later,students will have no exercise books to use.

B．Many years later,there will be no waste paper.

C．Many years later,the sandstorms will be weaker in Beijing.

D．Many years later,Beijing will be much dirtier.

It is none of your business _______ other people think about you.Believe yourself.

A．how

B．what

C．which

D．when

下列说法中，不正确的是( )。

A．个人与用人单位解除劳动合同取得的一次性补偿收入免税

B．退休人员再任职收入免税

C．单位为个人缴纳的补充养老保险免税

D．个人办理代扣代缴手续，按规定收取的扣缴手续费免税

60kg的人站在跷跷板某一位置时，跷跷板处于如图所示的平衡状态．由此可估测球的质量约为

A．20kg

B．30kg

C．60kg

D．120kg

简述DSS的结构特征。