一般炉膛爆炸都发生在燃油燃气锅炉的（）过程中
A、超压
B、降压
C、点火
D、正常燃烧
参考答案：C
石灰石管路堵塞的判断、处理。
—What did you do during your summer holiday?
—I spent my holiday _____ English in summer classes.
A. improving B. improves C. to improve
