阅读下面材料，在空白处填入适当的内容（一个单词）或括号内单词的正确形式。
Animals have been killed for their fur and feathers, and       (thousand) of kinds of animals have disappeared from the world forever. About 170 kinds in the US alone          (consider) in danger.
Why should people care?         we need animals, and if they are gone, there will never be any more. Every animal has its place in the balance of nature.         (destroy) one kind of animal can create many problems. For example, when farmers killed large numbers of hawks (老鹰), the farmers’ stores of corn and grain were destroyed        rats and mice. With no hawks to keep down their numbers, the rats and mice multiplied (繁殖)         (quick).
Luckily, some people are working         (help) save the animals. Some groups raise money to let people know about        problem. And they try to get the governments to pass laws protecting animals in danger. Quite a few        (country) have passed laws. These laws forbid the killing of any animals on the danger list. Slowly, the number of some animals in danger         (be) growing.