C

    Many people today like exercise. Some like to run, and some like to walk. Others dance or play balls. They do different kinds of exercise. Why do people like exercising? It's good for their health. And exercise helps make them tired, so they sleep better at night.

    You may like to run. If you do, take care of your feet. Make sure you have the right shoes. Some people like to run on roads, but they must watch out for cars.

    Walking is a good exercise. You may take a long walk in the park. It's more fun if you don't go alone. Go with a friend. The two of you may have a great time.

    Some people like to swim. But others don't like to go into the water. If you like this kind of exercise, make sure that someone is watching you. You must always take care when you are in the water. Jumping a rope (跳绳) or riding a bike is also good exercise. There are many other exercises. Find out what you like. You may need help at first. Some people often do exercise, and they can help you. Do exercise every day, and you will know what it makes you feel.

如图是验证人体呼出的气体中含有较多的二氧化碳的实验装置，瓶内均装入澄清的石灰水，请据图分析回答：

（1）如果吹气和吸气均选择弯管，在实验时，应向甲瓶____，向乙____ ．

（2）经向两瓶内分别吹气、吸气后，石灰水明显变浑浊的是____瓶；

（3）在本实验中，起对照作用的是____ 瓶．