下面说法正确的是( )。
A．不论是系统支持的线程还是用户级线程，其切换都需要内核的支持
B．线程是资源分配的单位，进程是调度和分派的单位
C．不管系统中是否有线程，进程都是拥有资源的独立单位
D．在引入线程的系统中，进程仍是资源调度和分派的基本单位
参考答案：C
解析：引入线程后，进程仍然是资源分配的单位。线程是处理器调度和分派的单位，线程本身不具有资源，它可以共享所属进程的全部资源。
Zoos Do a Good Job------ Maria Smith I know a large number of people think it is not wise to keep animals in zoos. __1__, I believe that it is good to keep animals in zoos. Firstly, zoos are places for people to see many different kinds of animals from all over the world. __2__ zoos, most people would never see a real bear or tiger. Secondly, zoos __3__ the animals very well. The animals are given food and cleaned regularly. In the wild (野外) , it is not always easy for an animal to find food, so sometimes it goes __4__. But animals kept in zoos never suffer from hunger. Thirdly, zoos protect the animals they take care of. They __5__ them safe places to live in. In the wild, some kinds of animals are in danger of becoming extinct (灭绝). But zoos give these animals a chance to live. There would be fewer kinds of animals in the world if there were no zoos. Zoos Are Unnatural ------Philip Black In my opinion, zoos are not good for animals; they are only good for people. It is not natural and __6__ to keep wild animals in cages. Most animals are kept in cages that are too small for them. In the wild, these animals would travel __7__. In zoos, they can’t do this. This is why the bears and tigers always look so sad. Most cages are not very clean, either. It is true that zoos give the animals food regularly, but this is not natural. Wild animals __8__ looking for their own food. We should treat animals in the same way that we treat other people----with respect. Would anyone be happy if you don’t let him go outside his home? Would Maria like to have lots of people standing outside her flat looking at her? No, she wouldn’t. And animals don’t like it, either. |