问题 选择题

某同学为探究黄瓜汁长期放置后维生素C含量的变化,分别向盛有等体积淀粉-碘溶液的两烧杯中滴加新鲜黄瓜汁和久置黄瓜汁,并记录使淀粉-碘溶液蓝色刚好褪去时所滴加的黄瓜汁的滴数,结果如下表(维生素C能使淀粉-碘溶液褪色).该实验说明

(  )

黄瓜汁新鲜久置
滴数1530

A.黄瓜汁中的维生素C具有氧化性

B.新鲜黄瓜汁中维生素C含量较高

C.久置黄瓜汁中维生素C含量较高

D.两者的维生素C含量一样高

答案

A、黄瓜汁中的维生素C具有还原性,不具有氧化性,故A错误;

B、新鲜黄瓜汁使淀粉-碘溶液蓝色刚好褪去时所滴加的黄瓜汁的滴数较少,而久置黄瓜汁中的维生素C能够被空气中的氧气氧化,使淀粉-碘溶液蓝色刚好褪去时所滴加的黄瓜汁的滴数较多,说明新鲜黄瓜汁中维生素C含量较高,故B正确;

C、久置黄瓜汁中的维生素C能够被空气中的氧气氧化,使淀粉-碘溶液蓝色刚好褪去时所滴加的黄瓜汁的滴数较多,说明久置黄瓜汁中维生素C含量较低,故C错误;

D、新鲜黄瓜汁使淀粉-碘溶液蓝色刚好褪去时所滴加的黄瓜汁的滴数较少,而久置黄瓜汁中的维生素C能够被空气中的氧气氧化,使淀粉-碘溶液蓝色刚好褪去时所滴加的黄瓜汁的滴数较多,说明新鲜黄瓜汁中维生素C含量较高,久置黄瓜汁中维生素C含量较低,故D错误;

故选B.

多项选择题
阅读理解

The key to reaching or staying at a healthy weight is regular exercise and good eating habits. Teens should get 60 minutes or more of physical activity a day. Note the word “activity”. As long as you’re getting your body moving, it doesn’t have to mean doing complicated exercises or going to the gym (体育馆) every day. All that matters is that each week you get the right balance of activity, including aerobic (有氧健身法的) strength building, and flexibility (柔韧性) exercise. Make exercise a habit by scheduling some every day.

On days when you have soccer practice or an aerobics class, you may have no trouble exercising for an hour or more. But most of us are busy, and 60 minutes a day of activity seems like a lot of time. The good news is that it’s OK to divide it into shorter “exercise breaks” throughout the day. Just as you might have a healthy snack to stop yourself getting hungry, exercise snacks can keep energy level high. So get up 15 minutes earlier and do some yoga or other stretching (伸展) activity. Fast walk or jog (慢跑) for 15 minutes at lunch. Do the same thing after school ­­­­­or walk or bike home. Add to that taking the stairs, gym class, and walking between classes during the day, and you’ve probably reached your 60 minutes.

Here are 5 simple ways to make an exercise lifestyle change:

1. Start today. Go outside for a walk.

2. Take the stairs instead of the elevator.

3. Instead of driving, walk or bike to places like school or a friend’s house.

4. Clean your room or wash the car.

5. Limit your time watching TV, using the computer, or playing video games--and when you do play, try some games that get you moving.

小题1: The underlined phrase “exercise snacks” in the second paragraph probably means ________.

A.food eaten before exercise

B.food eaten during exercise

C.shorter “exercise breaks”

D.a new kind of exercise小题2:Why should we have exercise snacks every day?

A.Because they can stop us getting hungry

B.Because they can keep energy level high

C.Because they can include many kinds of sports

D.Because they are more likely to relate to our daily life小题3:Which of the following is NOT mentioned in the passage?

A.To go hiking on your holidays

B.To spend less time on computer games

C.To go to school on foot or by bike

D.To do some housework at home小题4:What will be most probably discussed in the following paragraph?

A.Losing weight

B.Good eating habits

C.Exercising your brain

D.Outdoors exercise小题5: What would be the best title for this passage?

A.Regular exercise

B.School exercise

C.Indoors exercise

D.Difficult exercises