燃煤长管爆炸性实验，返回火焰长度大于400mm，为（）煤种。
参考答案：强爆炸性
—Is Mr. Black ill?
—______. I think he will have to stay at home to have a good rest.
A．I don’t think so
B．I’m afraid not
C．I hope so
D．I’m afraid so
科学思维的逻辑方法
