Animals are our friends.There are many many zoos in the 1. It's good to 2 animals in zoos.Zoos have many advantages, I think.

    Firstly, zoos are places for people to see 3 kinds of animals. Without zoos, most people would 4 see a real bear or tiger.

    5, zoos can take good care of animals. Zoos give 6 to animals and clean them on time every day. In the wild(在野外), it is not always easy for an animal to find food. So sometimes it goes 7^. But animals in zoos never go hungry.

    Thirdly, people protect the animals in zoos and offer them safe places to live 8^. Animals are living in zoos safely and happily. In the wild, some kinds of animals are 9 and are endangered(濒危的). But zoos give these animals a chance to live. Without zoos, there would be 10 kinds of animals in the world. People should do more things to protect animals.

如图，四棱锥S﹣ABCD的底面是正方形，SD⊥平面ABCD，SD=AD=a，点E是SD上的点，且DE=λa（0＜λ≤1）．

求证：对任意的λ=（0，1，都有AC⊥BE