The air in the house does not remain fresh very long. It.s because ______.
   A:the fresh air can.t come into the house
   B:there is only a little fresh air coming in and a little waste going out
   C:the air in the house can.t move at all
   D:the house gives off wastes
出自:河南科技大学大学英语3(专升本)

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