Mike worked for the Canadian government.One day, he was 1 to learn more about wolves.Do wolves kill lots of caribou (北美驯鹿)? Do they kill people?

    They gave him lots of food and clothes and guns.Then they put him on a plane and 2 him to a far-away place.The plane put him down and went away.There were no houses or 3 in this place, but there were lots of animals and lots of wolves.

    There are many 4 stories about wolves.Wolves are said to like to kill and eat people.Mike remembered these stories, and he was afraid.He had his gun 5him all the time.

    Then one day, he saw a group of wolves.There was a mother wolf with four baby wolves.A father wolf and another male wolf, younger than him, lived with them.

    Mike watched these wolves every day.The mother was a very good mother.She gave milk to her babies.She gave them lessons about life.They learned how to 6 food.The father wolf got food for the mother.The young male wolf 7 the children.They were a nice, happy family—a wolf family! Mike did not need his 8 any more.In a short time, he got on well with the family.Mike 9 them for five months.He learned that many stories about wolves were not true.Wolves do not eat people, and they do not eat many large animals.And he also learned bad things about 10.It was men who killed many caribou and wolves.

    Later, Mike wrote a book about wolves.He wanted people to understand them and stop killing them.

一种测定风作用力的仪器原理如图所示，它的不计质量的细长金属丝一端固定于悬点O，另一端悬挂着一个质量为m=1kg的金属球．无风时，金属丝自然下垂，当受到沿水平方向吹来的风时，金属丝将偏离竖直方向一定角度θ，风力越大，偏角越大．若某时刻金属丝与竖直方向偏角θ=30°，求此时金属球所受风力大小．（g=10m/s²）．