用棋子摆出下列一组“口”字，按照这种方法摆下去，则摆第13个“口”字需用棋子颗数为（   ）

通读下面的短文，掌握其大意，然后从各题所给的A、B、C三个选项中选出一个最佳答案。

Dear Sally,

    How are you? I'm happy that you can do the things you 1 at home. I never have fun, because there are too many 2 in my family. My parents are strict. I have to  3 at six o'clock every morning. And I have to make my bedroom4 before breakfast and then go to school. I can't play with my friends after school. I have to do 5 homework. After dinner I have to take the dog for    6 walk in the park. I can't watch TV on school nights. I have to  7 the violin for an hour. I can't go to bed late. I have to be in bed 8 nine o'clock. On weekends I have to clean my room and 9 the dishes. I also have to go to learn the violin on Sundays. I'm 10  tired. Can you help me?

                                                                                                                                                                    Yours,  

                                                                                                                                                                      Lisa

火力发电厂的燃料主要是煤，煤燃烧排放的SO₂、NO₂等污染物不仅污染空气，还会形成酸雨．邵阳市某发电厂处理NO₂的反应原理为CH₄+2NO₂=CO₂+X+2H₂O，则X的化学式是（　　）