A：莱茵河
B：多瑙河
C：塞纳河
D：伏尔加河
给下列句子选择合适的答语。
① How do you like this chess? ____ A. It's$50.
② How much is this sweater?____ B. Yes How much is it?
③ The socks are $50. ____ C. It's very pretty.
④ Can l help you? ____ D. They're too expensive.
天然气的主要成分是甲烷，常作燃料．甲烷完全燃烧的化学方程式可表示为：CH4+2O2CO2+2H2O．
CO2+2H2O．