下面四个整式中，不能表示图中阴影部分面积的是（   ）

从6名男同学，3名女同学中任选3名参加体能测试，则选到的3名同学中既有男同学又有女同学的概率为（　　）

    Dreams may be more important than sleep. Some people don't need much sleep. But they all need to dream, scientists say.

    Dreams take up about one quarter of our sleeping time. People have several dreams each night.

    Dreams are like short films. They are usually in color. They come to us over and over again. That may be because the dreamer is worrying about something. Dreaming may be a way of trying to find an answer.

    Some people get new ideas about their work from dreams. They could have been thinking about their work all day. These thoughts can carry over into dreams.

    Sometimes we wake up with a good feeling from a dream. But often we can't remember the dream. Dreams can disappear quickly from memory.

    Too many dreams can be harmful(有害的). The more we sleep, the longer we dream. The mind is hard at working when we dream. That is why we may have a long sleep and still feel tired after getting up.