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    My name is Lin Tao. I am a Chinese boy. Now I'm studying in America. There are many kinds of clubs here. When I first come here, I don't know anything about clubs. I'm a shy boy, so I can't speak English well. In my first year in America, I don't like to speak to others. In my second year I have to change (改变) myself by doing some new things. I realize that school is not just about getting good grades (成绩), it's also about being part of a club. One day, when I go to the Media Center with my classmate Jim, he tells me something about the club. It's interesting, so I join it. I am in many clubs now. It's good to be part of a club. These clubs help me to make new friends.

一般情况下，动物细胞没有的结构是（    ）

撒哈拉以南的非洲，在这片神奇而又充满生机的土地上，没有的是(       )

认识燃烧原理可以合理利用和控制燃烧反应。下列说法正确的是