《煤矿安全规程》第248条规定，火区内的氧气浓度降到（）以下时，方可认为火区熄灭。
A、3%；
B、5%；
C、8%
参考答案：B
It was in that country_____ he studied for his doctor's degree____he fell in love with the girl. [ ]
A. that; that
B. which; where
C. where; that
D. where; where
与台班折旧费计算无关的是（）。
A．残值率
B．物价上涨系数
C．耐用总台数
D．时间价值系数
