送煤气不着火或着火后又熄灭应如何操作？
参考答案：
送煤气时不着火或着火后又熄灭，应立即关闭煤气阀门，查清原因，排净炉内混合气体后，再按规定程序重新点火。
“ Can you speak English ?”“ Of course , I have studied it ___ I was six years old.”
A. though B. since C. before.
发现热轴的四个基本环节是什么？
