每半扇发动机反推上有几个反推折流门？（）
A、2个
B、4个
C、6个
D、8个
参考答案：C
请根据句意,用括号内所给词的适当形式填空。
1.My mother takes me to Da Tonghua Suppermarket_____(two)a month.
2.I have an e-friend____(call) David.
3.I broke your bike, I'm _____(real)sorry for it.
4.My favourite _____(play) are Yao Ming and Liu Xiang.
5.Who teaches_____(they)Maths this term?
氢气发生器(利用水电离原理产生氢气)
