Many animals hide to stay alive. They hide in many ways. Some animals hide in leaves; some animals hide in snow. Usually their colors or shapes help protect them. It's hard to see an Arctic bear in snow. Its white fur helps protect it. Chameleons(变色龙) can hide by changing colors. Their skin turns the same color as what is around them. Some chameleons can change colors in five minutes.

    Many animals try to look bigger than they are to stay alive. Some animals can make other animals think they are very big. If they look very big, animals that are looking for food will run away. Bears can walk on two legs. They look very, very scary. Some animals will run away from them.

Many animals try to stay around other animals. This helps them stay alive. Zebras stay close together so that they can help each other look out of danger. Seeing many stripes at once can also confuse animals that want to eat them. Some birds stay in a circle, each toward a different direction. In this way they can also help each other stay alive by looking around for animals that many want to eat one of them.

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.

    Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back. Plants certainly cannot run away, and they have no teeth or claws. But plants can protect themselves in both physical and chemical ways.

    Some plants have their own ways to keep animals away. For example, the leaves of the holly(冬青) have sharp prickles(刺) that discourage grass-eating animals. Holly leaves on lower places have more prickles than leaves on upper places. This is because the lower leaves are easier for most animals to reach. Some plants, such as the oak trees(橡树), have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material, and eating such grasses wears down the animals' teeth. Many plants also have chemical defenses. Some plants produce chemicals that taste bitter(苦) or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a worm bites a tobacco leaf (烟叶), the leaf produces a chemical smell. Many plants depend on both physical and chemical defenses. A certain plant in China, for instance, has prickly leaves, and each prickle has poisonous water(毒液). Only one experience with this kind of plant will teach an animal to stay away from it in the future.

    Like humans, dogs donate blood too, and not every dog can donate blood. The dogs are screened(检查) for health first. Dogs must have the correct blood type, weigh at least 55 pounds and be younger than 8 years old. They may donate three or four pints(品脱) a year, which can help animals that are suffering from illnesses like cancer or an accident like being hit by a car. One pint can save up to three dogs.

    Owners volunteer their pets for the short procedure (程序), which requires no sedative, a kind of medicine given to calm him or her down. It's the dog that finally chooses to lie still and give. If the dogs want to get up and leave, they can.

    Sandy Lucas brought her 7-year-old black German shepherd, Rains, to the bloodmobile(流动血站) when it was parked at her small village. Sandy said she wouldn't have troubled herself with highway traffic and city parking problems to take the dog to Penn Vet's animal hospital in downtown Philadelphia, which is twice as far as her home. But the bloodmobile made it easy to find out if Rains could donate. "I was very, very excited that she had the right blood that was needed to help another dog out," said Sandy. "We'll surely do it again."

    There are millions of stars and planets in space. What's the difference between stars and planets? Stars can give out heat and light, but planets cannot.

    The sun is one of the stars. Some planets are balls of rock and some are balls of gas. We live on the planet earth. The earth spins around once every day to give us day and night. The earth goes around the sun once every year to give us different seasons.

    There are eight planets moving around the sun. We call the family of the sun and its planets the solar system. Mercury is the nearest to the sun, so it is very hot. It is the smallest planet. Venus is very bright and hot. It is the nearest to the earth. Mars is covered with orange-red desi and rocks, so it looks like a red star in the sky. It has seasons like the earth. Jupiter has more than 16 moons （卫星）and it is the biggest and heaviest planet. Saturn has more than 22 moons. The other planets, such as Uranus and Neptune, are all very far from the sun and very cold. We need a telescope（望远镜）to see them.