采用先拱后墙的衬砌，墙顶与拱脚的封口应在墙灌筑（）后进行。
A、2h
B、12h
C、24h
D、48h
参考答案：C
Where____live before you came here? [ ]
A. did you used to
B. did you use to
C. use he to
D. he used to
烟机出口温度高的现象是什么？
