控制介质单向流动的阀门是（）。A、截止阀 B、闸阀 C、止回阀 D、旋塞阀

                     My favorite animals
Elephants are my favorite animals. I often go to __1____ them in the zoo ___2___ my parents. They are our friends. They ___3__ in Africa. They are very clever, so I ___4___ them very much. They like to play with their friends. They are useful. They can ___5___ people do some things. They are our friends.