Parents today also worry about their children's diets. Some doctors give the following advice：

A

    Everyone knows that exercise is important. It makes your heart and body strong. But you need to know the following.

*Get your body ready!

    Before you do any exercise, be sure to warm up for at least five minutes. During warming up, you should stretch(伸展) all parts of your body.

*Exercise enough, but not too much.

    It's good to exercise twice each week. Thirty minutes each time is enough. Try all kinds of things until you find one, two or even three sports that are right for you.

*Exercise at fitness centres.

    There is a lot of equipment(设备) at fitness centres. The equipment will help exercise your arms, legs and other parts of your body to make you fit. Some people buy equipment. But it is very expensive.

*Stop playing when you are hurt!

    If you get hurt when you are doing exercise, don't play again until you are well.

*Don't get thirsty!

    Drink a lot of water when you are playing sports because it is easy to become thirsty.

Find Which Direction Is South

    Do you have a good sense of direction? If not, please take with you a compass. But if you forget to take a compass, you can still find your way.

    It's never a good idea to imagine that the family member who was entrusted (委托) with the job of map-reading actually knows where the family is. You can tell by the slightly confused load on their faces that nothing on the ground seems to match the map. Never mind. The sun is shining and it's still morning.If you don't know the exact time, you can still find out where south is, but you'll need to be patient.

    ①Find a straight stick and put it in the ground in a place where you can mark its shadow.

    ②Try to position the stick as vertically(垂直)as you can. You can check this by making a simple plumb line (铅锤线) with a piece of string and weight. You haven't got any string? OK, use a thread from your clothes with a button tied at the end to act as a weight.

    ③Mark the end of the shadow cast by the stick.

    ④Wait approximately half an hour and mark the end of the shadow again.

    ⑤Keep doing this until you have made several marks.

    ⑥The mark nearest the stick will represent the shortest shadow, which is cast at midday, when the sun is highest in the sky and pointing to the exact south.

    ⑦Pick a point in the distance along the line between the shortest shadow and the stick.

    ⑧That point is south of where you are.

    ⑨Now you can turn the map, like you did before, and find which way you should be travelling.

    Why do plants grow in some places and not in the others? Why does some land have so much growing on it, while other land has almost no plants growing on it at all?

    To grow, plants need several things. One is warmth. In very cold places almost nothing grows. Plants also need water. In very dry parts of the Earth only a few unusual plants can grow. That's why dry deserts everywhere are almost not covered by trees or grass.

    Plants must also have a place in which to put down their roots and grow. They find it difficult to grow on hard land. The town is built on hard land. The plants here have only the soil found between the cracks of the stones to grow in.

    Another thing plants must have before they can grow is food.

What will happen if we try to make things grow on the sandy beach? A few plants, such as beach grass, will grow in sand, but most plants won't. Even if the weather is warm enough and we water the plants each day, many of them will die because the sand on this beach has almost no food for plants.

    Here is some information about some of the wonders of the world. I am sure you will be interested in them.

    ThePyramids of Egypt

    There are about eighty pyramids known today. The most well-known was for Pharaoh（法老）

    Khufu. It is known as the "Great Pyramid". It's also the largest one. Workers used about 2.3 million blocks of stone to build it. They spent about 20 years finishing it.

    The Hanging Gardens of Babylon

    The garden sat on a hill. It was a large and wonderful structure（建筑物）. Many parts of the garden were high up on large columns（支柱）. There were many big and green trees with lovely flowers. Although there are many different ideas about the garden, we are not sure whether this wonder ever existed（存在）!

    TheLighthouse of Alexandria

    The Lighthouse of Alexandria was designed about 2,000 years ago. It was in Egypt, too. It was one of the ancient wonders of the world, about 135 metres high. It was once the highest building in the world. Although it doesn't exist now, many people come to see its relic（遗址）every year.

    Solar storms shake Earth's magnetic field(磁场). They not only influence human technology, but also animals, reported Forbes.

    Studies show that many animals use changes in Earth's magnetic field to find directions. These changes provide the animals a general compass(指南针) for south and north. Animals can also use them as landmarks.

    For example, scientists have found special cells in part of a bird's eye nervous system(神经系统). They seem to react to changes in the magnetic field.

    Some fish species, like the common trout，have cells with magnetic sensors in their nasal cavity(鼻腔). In 1994 "magnetic sense" was also discovered in sea turtles.

    Some whale species may use magnetic sense to navigate (导航) the oceans. A dysfunction of this sense may explain the still mysterious beachings (动物搁浅). Sometimes several hundred animals, such as whales and dolphins, are driven out of water along beaches. They usually can't breathe under their own weight and die slowly.