自尊是人人都需要的，因为（    ）

①自尊是一种健康的心理状态，让我们感悟生活的意义    ②自尊的人看重自己，让我们体验到自我价值

③自尊让我们被人尊重，体验快乐与感动                            ④自尊促使我们努力奋发有为，实现人生价值

    Hello, my name is He Lin. I'm in Class2, Grade 7. There are forty-three students in my class, nineteen girls and ____ （二十四）boys. There is a ____ （电脑）on the teacher's desk and a TV in the____ （前面）of the classroom. Are there any photos on the classroom walls? Yes, there are. But there ____ （没有）a map of China or a map of the world on the wall. What about your class? How ____（多少）students are there in your class?

DNA分子完全水解后，得到的化学物质是(     )