题目

孟德尔利用豌豆作为实验材料进行植物杂交实验，成功地发现了生物的遗传规律。下列各项中不能作为豌豆作为遗传实验材料的优点是（      ） A. 豌豆是严格的闭花自花授粉植物    B. 豌豆在自然状态下一般是纯种   C. 豌豆具有许多明显的相对性状        D. 杂种豌豆自交后代容易发生性状分离as, sleep ,dream, like, again, about, think, must, wake up, quick, much ,why "Dreams (梦 ) may be more important than sleep. We all need to dream," some scientists say. Dreams take up about one quarter of our 1 .________ time. People have several 2. ________each night. Dreams are like short films. They are usually in colour. Some dreams are 3. ________ old films. They come to us over and over 4. ________. 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 5. ________ their work from dreams. They may have been 6. ________ about their work all day. These thoughts can carry over into dreams. Sometimes we 7. ________ with a good feeling from a dream. But often we can't remember the dream. Dreams can disappear (消失) 8. ________ from memory (记忆). Too much dreaming can be harmful (有害的). The 9. ________ we sleep, the longer we dream. The mind is hard at work when we dream. That is 10. ________ we may have a long sleep and still wake up tired.