问题 问答题

(超市中的许多食物用保鲜膜包装后出售.保鲜膜为什么可以“保鲜”呢?

[设计实验]在A、B、C三只相同的玻璃杯中,分别注入等体积的蒸馏水,并在各玻璃杯外壁标明刻度,如图所示放置一周.

[实验现象]一周后发现:A杯中的水量几乎不变;而C杯中的水量减少较多;B杯中的现象是______.

[解释]请用分子的知识解释C杯中水量减少的原因:______.

[结论]保鲜膜除了可以阻止食物中水分流失,还能隔绝______,防止食物腐败.

[提出新问题]制作保鲜膜的材料是热固性塑料还是热塑性塑料呢?

[实验]在一只试管中放入少量保鲜膜碎片,用酒精灯缓缓加热,观察到碎片熔化,冷却后变成固体,加热又可以熔化.由此得出:制作保鲜膜的材料是______(填“热塑性”或“热固性”)塑料.

[反思](1)保鲜膜虽然能延长食品的保鲜期,但大量使用后丢弃会造成______,所以要控制使用.

(2)化学物质可以造福人类,但有时也会给人类带来危害,请你再举一例说明______.

答案

[实验现象]塑料不透水,纸的透水性差,可以透过少量的水,所以B杯中的现象是:水量减少比A杯多,比C杯少.

[解释]水是由水分子构成的,水分子是不断运动的,杯中的水分子运动到了杯外.

[实验]塑料的透水、透气性很差,可以阻止食物中水分流失,还能隔绝氧气(或空气),防止食物由于缓慢氧化而腐败.

[反思]根据“保鲜膜碎片用酒精灯缓缓加热,观察到碎片熔化,冷却后变成固体,加热又可以熔化.”的信息可知,这种塑料有热塑性.

(1)难降解塑料长期堆积会污染土壤,污染地下水,危害海洋生物生存,燃烧还会产生有害气体.

(2)事物都是“一分为二”的,化学物质也是这样,有利的同时也有害,如二氧化碳可以灭火,但也能产生温室效应.

故答案为:[实验现象]:水量减少比A杯多,比C杯少;

[解释]:氧气(或空气);

[实验]:热塑性;

[反思]:(1)白色污染;

(2)二氧化碳可以灭火,但也能产生温室效应.

问答题
阅读理解

Some students get so nervous before a test, they do poorly even if they know the material. Sian Beilock has studied these highly anxious test-takers.

Sian Beilock: “They start worrying about the consequences. They might even start worrying about whether this exam is going to prevent them from getting into the college they want. And when we worry, it actually uses up attention and memory resources.I talk about it as your cognitive horsepower that you could otherwise be using to focus on the exam.”

Professor Beilock and another researcher, Gerardo Ramirez, have developed a possible solution. Just before an exam, highly anxious test-takers spend ten minutes writing about their worries about the test.

Sian Beilock: “what we think happens is when students put it down on paper , they think about the worst that could happen and they reappraise the situation. They might realize it’s not as had as they might think it was before and, in essence(本质上), it prevents these thoughts from popping up when they’re actually taking a test.”

The researchers tested the idea on a group of twenty anxious college students. They gave them two short math tests. After the first one, they asked the students to either sit quietly or write about their feelings about the upcoming second test.

The researchers added to the pressure. They told the students that those who did well on the second test would get money. They also told them that their performance would affect other students as part of a team effort.

Professor Beilock says those who sat quietly scored an average of twelve percent worse on the second test. But the students who had written about their fears improved their performance by an average of five percent.

Next, the researchers used younger students in a biology class. They told them before final exams either to write about their feelings or to think about things unrelated to the test.

Prefessor Beilock says highly anxious students who did the writing got an average grade of B+, compared to a B- for those who did not.

Sian Beilock: “What we showed is that for students who are highly test-anxious, who’d done our writing intervention, all of a sudden there was no relationship between test anxiety and performance. Those students most likely to worry were performing just as well as their classmates who don’t normally get nervous in these testing situations.”

But what if students do not have a chance to write about their fears immediately before an exam or presentation? Professor Beilock says students can try it themselves at home or in the library and still improve their performance. 

小题1:What may happen if students have the problem of test anxiety?

A.Test anxiety can improve students’ performance to some degree.

B.Students’ attention and memory resources run out when worried.

C.Students may not be admitted into their favorite college if worried

D.Test anxiety is sure to cause students to fail the test.小题2:Which of the following if TRUE?

A.In the first math test, students who sat quietly performed better.

B.In the second math test, students who wrote about their feelings did worse.

C.Some college students are highly anxious test-takers while others are not in the tests.

D.The result in the math test agrees with that in the biology test.小题3:What does the underlined phrase “popping up” mean?

A.Giving out

B.Fading away

C.Becoming clearly

D.Appearing suddenly小题4:what is most probably Sian Beilock?

A.A psychology professor.

B.A philosophy researcher.

C.A politics professor

D.A tutor小题5:What is the main idea of the passage?

A.It is a common practice for students being worried before a test.

B.Being worried before tests does harm to students’ performance.

C.Anxious students overcome test anxiety by writing down fears.

D.It is important for students to overcome test anxiety.