问题 选择题

已知X、Y、Z、W四种短周期主族元素在周期表中的相对位置如图所示,其中X原子最外层电子数是其电子层数的2倍。下列说法正确的是

A.四种元素的原子半径大小rY>rW>rX>rZ

B.元素X的含氧酸只有一种,元素Y则有两种

C.元素Z的气态氢化物的稳定性比元素Y的强

D.元素Y和W的氧化物是导致酸雨的主要原因

答案

答案:D

题目分析:X、Y、Z、W为四种短周期主族元素,根据在周期表中的相对位置,X位于第二周期,X原子最外层电子数是其电子层数的2倍,则X为C元素,可推出Y为N元素、Z为Si元素、W为S元素。A、根据四种元素的相对位置,原子半径大小顺序为:rZ > rW> rX>rY,错误;B、C的含氧酸为羧酸,有多种,错误;C、根据元素周期律,元素Z的气态氢化物的稳定性比元素Y的弱,错误;D、S的氧化物和N的氧化物是导致酸雨的主要原因,正确。

单项选择题
阅读理解

阅读理解。

     The meaning of the word "volunteer" may be a little different in different countries, but it usually means

"one who offers his or her services." There are many different ways in which people can volunteer, such

as taking care of sick people, working in homes for homeless children, and picking up garbage (垃圾) from

beaches and parks. Volunteers may work within their own countries or in other countries. They are often

people with a strong wish to help those who are less fortunate than themselves. Volunteers don't expect any

kind of pay.

     At the root of volunteering is the idea that one person may have the ability to offer services that can help

other people. Tracy, a good friend of mine, however, recently came back from India with a new idea of

what being a volunteer means. She worked for two and a half weeks in one of Mother Teresa's homes in

Calcutta. The following is her story.

     "I first heard about Mother Teresa in my high school, we watched a video (录像) about her work in India

and all over the world. I was so moved by her spirit to help others and her endless love for every human being

that after I graduated from high school, I too wanted to try her kind of work. So with two friends I flew to

Calcutta for a few weeks."

     "I was asked to work in a home for sick people. I helped wash clothes and sheets, and pass out lunch.

I also fed the people who were too weak to feed themselves and tried to cheer the up. I felt it was better to

share with them than to think that I have helped them. To be honest, I don't think I was helping very much.

It was then that I realized that I had not really come to help, but to learn about and experience another culture

(文化) that helped improve my own understanding of life and the world."

1. According to the text, a volunteer refers to a person who _____.

A. is willing to help those in need without pay

B. can afford to travel to different places

C. has a strong wish to be successful

D. has made a big fortune in life

2. Tracy started her work as a volunteer _____.

A. after she met Mother Teresa

B. after she finished high school

C. when she was touring Calcutta

D. when she was working in a hospital

3. Why did Tracy choose to be a volunteer?

A. She liked to work with Mother Teresa.

B. She had already had some experience.

C. She was asked by Mother Teresa's example.

D. She wanted to follow Mother Teresa's example.

4. What is Tracy's "new idea" (Paragraph 2) of being a volunteer?

A. Going abroad to help the sick.

B. Working in Mother Teresa's home.

C. Doing simple things to help the poor.

D. Improving oneself through helping others.