浓度达到（）时瓦斯爆炸最剧烈。
A.7.5％
B.8.5％
C.9.5％
D.10%
参考答案：C
You must use ______ to open the bottle. Or you can borrow a bottle opener from the neighbor.[ ]
A. strength
B. force
C. power
D. energy
C．由君主制变成了共和制
