问题 选择题

已知CsCl晶体的密度为ρg/cm3NA为阿伏加德罗常数的值,相邻的两个Cs的核间距为acm(如右图所示),则CsCl的相对分子质量可表示为

A.

B.

C.

D.NA·a3·ρ

答案

答案:D

根据氯化铯的晶胞可知,该晶胞中含有8个氯离子和铯离子,所以有

,解得M=NA·a3·ρ,所以答案选D。

阅读理解

You may feel curious (好奇的) about students in other countries: Do they also have so much homework? What do they do in their spare time? On April 8, a report came out on the lives of high school students in China, Japan, South Korea and the US. It surveyed around 6,200 students from the four countries last year. You will find the answers to many of your questions in this report.

Who studies hardest?

Chinese students spend the most time studying. Nearly half of Chinese students spend more than two hours on their homework every day. That’s much more than students of the US (26.4%), Japan (8.2%) and South Korea (5.2%).

Who sleeps most often in class?

Japanese students fall asleep in class most often. About 45% of them said they sometimes doze off (打瞌睡) in class. In South Korea, it’s 32%; in the US, 21%; and 5% in China. South Korean students don’t like taking notes. About 70% said they write down what the teacher says in class, many fewer than in Japan (93%), China (90%) and the US (89%).

Who is the most distracted (分心的)?

American students are the most active in class, but also the most distracted: 64.2% said they chat with friends in class; 46.9% said they eat snacks in class; and 38.9% said they send e-mails or read unrelated (无关的) books in class.

What do they do after school?

In their spare time, most Chinese students study or surf the Internet. Most American students hang out with their friends. Most Japanese students do physical exercises. Most Korean students watch TV.

小题1:Who spent the most time studying according to the passage?

A.Chinese students

B.American students

C.Japanese students

D.Korean students小题2:American students fall asleep in class most often, don’t they?

A.No, they aren’t.

B.Yes, they are.

C.Yes, they do

D.No, they don’t.小题3:Who like taking notes most according to the passage?

A.Chinese students

B.American students

C.Japanese students

D.Korean students小题4:Which of the following sentences is wrong?

A.In their spare time , most Chinese students surf or study the Internet.

B.American students sometimes chat with friends in class.

C.A few Japanese students do physical exercises.

D.It surveyed around 6,200 students from the four countries last year.

单项选择题