防火、灭火、自救等安全知识是每个人都应该了解的生活常识，下列做法错误的是（　　）

公有制为主体、多种所有制经济共同发展，是我国社会主义初级阶段的一项基本经济制度。必须坚持和完善这一基本经济制度的根本原因是

作文。

题目：第一次_____

每个同学都有许许多多的第一次，如，第一次做饭，第一次参加比赛，第一次坐火车旅游，第一次吃螃蟹……各种各样的第一次，哪一个“第一次”给你留下的印象最深刻，请你写下来。

要求：①把题目补充完整。

②要突出“第一次”这个特殊的情境；要把事情的经过按顺序写清楚，写具体；表达出自己的真情实感。

③不少于300字。

分子和原子的主要区别是（）

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    According to a recent survey, British teenagers are not in good health because they don't have enough time for sleep. They don't sleep well, either. They are often disturbed(打扰) by electronic gadgets(器具，装置) in their bedrooms. We call such kind of sleep “junk sleep”.
    We did a survey among 1,000 students aged 12 to 16, and we found out that 30 percent of them slept for only 4 to 7 hours a day. Nearly a quarter said they fell asleep while they were watching TV, listening to music or using other electronic gadgets.'
    Nowadays, almost all the teenagers have a phone, music system or TV in his or her bedroom. Almost 20 percent of the teenager boys said the quality of their sleep were not good. It was affected by leaving their TVs or computers on. The survey also found out that 40 percent of young people felt tired every day. What's more, the girls aged 15 to 16 felt the worst among them.
    “Teenagers need to realize the importance of sleeping well. If they sleep well, they will be able to study hard and perform well at school. I am shocked to know that so few teenagers have noticed the close connection between sleep and schoolwork,” said Dr Chris.