—Sam, you have made so _________ progress in English. Congratulations!

—Thank you. [ ]

A. several

B. many

C. little

D. much

在煤矿井下正常通风情况下，爆炸威力最强烈的实际瓦斯浓度为（）左右。

A、7%

B、8%

C、9.5%