How to Become Fit?
Healthy eating habit along with regular exercise is the only way to become fit. If you have the correct number of calories and exercise regularly, you will lose weight, keep fit, and feel great, too.
During your teenage years, it is important to give your body the energy it needs. If you skip (跳过) meals, you won’t get enough calories, and then you will feel tired. By the way, calorie is just another word for energy. About 50% of your calories should come from rice, bread, vegetables and fruit. You also need to drink a lot of water, 6 to 8 glasses a day. Water helps keep your system clean. Drinking enough water will make your skin better and make you healthy.
Exercise is something that can help to make you look good, feel good and be healthy. Experts suggest that teenagers spend at least 30 minutes exercising, five times a week. That is easy to do! You can walk or ride your bike to school, and do sports at school. However, teenagers often give up sports, saying they have no time left after their studies. In fact, doing exercise can help them sleep better at night and increase their ability to focus on their study.
If you follow the suggestions above, you will look and feel much better and become fit.
【小题1】 What’s the main idea of this passage?

How did ancient people tell time?

◆Natural ways of keeping time

In ancient time，people had to use the sun and the moon to tell time．They got up when the sun came up and worked in the fields until the sun went down．

◆Man-made things

The sand clock is made of two glass balls joined by a narrow neck．The top ball was filled with sand．The sand slowly moved through the neck into the bottom（底部）ball．People knew the time by watching how much sand fell to the bottom hall．People also made the water clock．They made a small hole near the bottom of a pot．when the water in the pot dripped（滴）out，marking（刻度）inside the pot showed how much time passed．

◆Body clocks in living things

Animals' body clock

Animals don't need clocks to know time．They have their body clocks．Birds know when to fly to warmer places before winter．Some animals know when to keep more food for the winter．Some fish know when it's time to move up the river and lay eggs．

Plants' own clock

Plants have their own clocks to keep time．Plants know when to open flowers or when to drop their leaves．

Body clock in human beings

People also have their own body clocks．When we get used to our lives，our body clocks can be very exact．It can tell us when it's time to wake up．It can also tell us when to eat or to go to sleep．

1．How could an ancient farmer know when to go back home from the field in the daytime?

A．By looking at the moon．                         B．By the sand clock or the water clock．

C．By looking at the sun．                               D．By feeling whether tired or not．

2．According to the passage，how can animals know time?

A．They use body clocks．                           B．They ask other animals．

C．They use the sun and the moon．                D．They make something to tell time．

3．How many kinds of living things with body clocks are mentioned here?

A．Two．                B．Three．               C．Four．                   D．Six．

4．In what way is the sand clock the same as the water clock in telling time?

A．Both of them have a neck．

B．Both of them have two glass balls．

C．Both of them can be used only once．

D．Both of them give the time by quantity（数量）．

5．The passage is mainly about _________．

A．man-made clocks                                    B．nature's clocks

C．time and clock                                           D．how people keep time