题干

阅读下列材料,回答问题。

材料一 1945年7月美国引爆第一颗原子弹

材料二 1949年苏联第一颗原子弹爆炸

材料三 美、苏战略核力量对比(1970年)

国家

陆基洲际导弹

潜射导弹

战略核弹头

战略轰炸机

美国

1054

656

4000

550

苏联

1300

240

1700

150

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    My friend,Victor,is a zoo keeper in the National Zoo.His work is very interesting but it is hard.Sometimes it is dangerous,too.Every morning,the zoo keepers have to get up at five to prepare the food for the animals.Each kind of animal eats special food.For example,the lions must be given meat; the deer must be given grass and leaves; and the parrots must be given fruit and nuts.Sometimes some animals won't let the others eat their food.If this happens,each of them must be fed separately(分离的).
    Every morning each cage (笼子) must be washed by the zoo keepers.This can be dangerous,especially with lions and tigers.To make the work easier,the animals are locked in the sleeping compartments( 隔间) while the cages are being washed.When the animals are sick,the zoo keepers must look after them.Each sick animal is kept in a separate cage and given medicine.Sometimes they must be given injection.It is not easy to inject a sick lion!
    All the keepers live near the zoo.Each of them has a small house.There he lives with his family.They do not have holidays on Sundays and special holidays.Instead,each of them has a day off during the week.Each keeperhas a holiday on a different day from that of the other keepers.
    The most important job of the keepers is to look after the safety of the visitors.People must be stopped from doing dangerous things.Many people have been hurt because they did careless things,like putting their hands into the lion's cage.