我们按____、____、____ 、____和____对天气现象进行分类。

根据短文理解，选择正确答案。

     Canada you can find dogs, cats, horses etc, in almost every family. These are their pets. People love these pets and pets are their good friends. Before they keep them at their houses, they take them to animal hospitals to give them needles(针)so that they won't carry disease(疾病). They have special animal food stores, though(尽管)they can get animal food in almost every store. Some people spend about two hundred Canadian dollars a month on animal food.

    When you visit people's homes. they would be very glad to show you their pets .You will also find almost every family has a bird feeder (喂食器) in their garden. All kinds of birds are welcomed to come and have a good meal. They are free to come and go and nobody can kill any animals in Canada. They have a law against killing wild(野生的) animals. If you killed an animal, you would be punished(处罚). If an animal happened to get run over by a car, people would be very sad about it.

    People in Canada have many reasons to like animals. One of them is: When children grow up, they leave their parents and start their own work and life. Then their parents will feel lonely, but pets can help them. They can be good friends and never leave them alone.

已知等差数列{a_n}的前n项和为S_n=n²+pn+q（p，q∈R），且a₂，a₃，a₅成等比数列．