有煤与瓦斯突出危险的采掘工作面，必须安设（）。
参考答案：甲烷断电仪
19．We were that the Wenchuan earthquake left the whole city in ruins.
A．shocked
B．worried about
C．worrying
D．Shocking\]
单子叶植物茎的构造有哪些特点？
