关于机械送风系统进风口的位置，应符合的要求是（） A.应设在室外空气较清洁的地点 B

                                                            A cat and a rat
     There is a folder (夹子) in the room. There is a fish on it. A rat comes out. He sees the fish.
     There is also a cat in the room. He comes out, he sees the rat. He comes at the rat.
      "Don't eat me," says the rat to the cat, "You like fish. I have a nice fish for you. Look, it is."
      The cat lets the rat go. He comes up to the fish. Oh, the folder catches one of his paws (爪子).