People keep dogs and cats as pets because they are friendly. Now there are also lots of people who like keeping goldfish as pets. Goldfish are not like dogs or cats. They are not any trouble and they are good-looking. People are happy to watch them swim around in the tank(鱼缸). If you want to keep them as pets, I think there is something to learn about before buying one.

The fish need a comfortable tank. Make sure the tank is large enough. Then the goldfish can swim in it freely(自由地). Keep the tank clean. But never clean it with soap. Hot water is OK.

Dirty water is not good for the health of the goldfish. If the water is dirty, the goldfish will easily get ill. Change some water once a week, but never change all of the water because there is something that your goldfish need. Put a few snails(蜗牛) in the tank. They have abilities to keep the water clean.

There are many different kinds of special fish food in pet shops. They are good for your goldfish. You should feed your goldfish with the special food only once a day. Also it is important not to give them too much food.

Keep goldfish as pets

The polar bear is a very big white bear. We call it the polar bear because it lives inside the Arctic Circle(北极圈) near the North Pole(北极). There are no polar bears at the South Pole.

At the North Pole there is only snow, ice and water. There is not any land. The polar bear lives in the snowy and icy world. You cannot see the polar bear clearly in the snow because its coat is yellow-white. It has a very warm coat because of the cold weather in the Arctic Circle.

The bear is 3 meters long and it weighs 450 kilos. It can stand up on its back legs because it has very wide feet. It can use its front legs as arms. The polar bear can swim 120 kilometers in the water. It catches fish and sea animals for food. It goes into the sea when it is in danger.

Some people kill the polar bear for its beautiful white coat. The governments of Canada and the United States say that no one is allowed to kill polar bears now. They don’t want all of these beautiful animals to die.

Many people use many expressions（表达法）with the word dog. They love their dogs and treat them well. They take their dogs for walks, let them play outside and give them good food and medical care. However, dogs without owners to care for them live a different kind of life. The expression, to lead a dog’s life, describes a person who has an unhappy existence（存在）.

Some people say we live in a dog-eat-dog world. That means many people are competing for the same things, like good jobs. They say that to be successful, a person has to work like a dog. This means they have to work very hard. Such hard work can make people dog-tired. And, the situation would be even worse if they became sick as a dog.

Still, people say every dog has its day. This means that every person enjoys a successful time during his or her life. To be successful, people often have to learn new skills. Yet, some people say that you can never teach an old dog new tricks. They believe that older people do not like to learn new things and will not change the way they do things.

Dog expressions also are used to describe the weather. The dog days of summer are the hottest days of the year. A rainstorm may cool the weather. But we do not want it to rain too hard. We don’t want it to rain cats and dogs.