问题 选择题

下列一定属于纯净物的是………………………………………………(  )

A.由同种分子构成的物质

B.由不同种分子构成的物质

C.由同种元素组成的物质

D.由不同种元素组成的物质

答案

答案:A

右同种分子构成的物质一定时纯净物,不同种分子构成的物质是混合物,右同种元素组成的物质可能是混合物,如石墨和金刚石的混合,不同种元素组成的物质可能是混合物也可能是纯净物,所以答案选A。

阅读理解

阅读理解。

     What would you think if you went back to school on Monday and there were no desks or chairs in your

classroom?

      That's what some fourth-and-fifth-graders at a school in Minnesota discovered earlier this year when they

took part in a research project to see if changing their classrooms would make them more active.

     Researchers from the Mayo Clinic were concerned about reports that as many as half of American kids

could be seriously overweight-or obese-by the year 2010. So they set up a different kind of classroom, which

you might see in the future.

      Instead of desks, the Elton Hills Elementary students had adjustable work stations where they could stand,

kneel on mats or sit on big exercise balls. Students were given laptops and iPods that allowed them to move

and learn at the same time.

     Sensors (传感器) were attached to the kids' legs to calculate how many calories students burned in their

new set-up.

      Their typical school day was probably not anything like yours. One group of students downloaded an

audio file (有声文件) of their teacher reading a book; they listened to it while walking for exercise. Another

group took a spelling test by listening to their iPods.

     Some students liked the freedom, but others missed the traditional classroom.

     "I don't like standing up," Mariah Matrious said."My legs get tired, and I like sitting down." So, did the

experiment work? Researchers still are studying the data, but early results indicate that the kids did move

around more in the new classroom.

     "It showed us that, given the opportunity to move, kids will move," said researcher Lorraine

Lanningham-Foster.

     That's important because studies have shown that even simple movement-climbing stairs instead of taking

an elevator (电梯), for example, or washing dishes by hand instead of loading the dishwasher-can be as

important as formal exercise when it comes to controlling one's weight.

1. The school in Minnesota carried out the research _____.

A. to punish the badly performed students

B. to prevent children from being too fat

C. to spare a lot of money for the state

D. to meet the needs of different children

2. The newly designed classrooms are different from the traditional ones EXCEPT that _____.

A. there were no desks and chairs

B. the students can move and learn at the same time

C. students in different groups are given different tasks

D. teachers don't necessarily instruct the students

3. According to Lorraine Lanningham-Foster, _____.

A. the research got some expected results

B. the experiment needs further changes

C. not everyone liked the freedom of this new style

D. The students should be taught without classrooms

4. What would be the best title for the text?

A. No Desks or Chairs in the Classroom

B. New Classrooms in the Future

C. School Takes a Stand Against Obesity

D. Washing dishes by hand in the Classroom

单项选择题