发散思维的主要特征有：______、变通性、______。
参考答案：流畅性，独特性
—Don't forget to phone me when you get to New York.Just let me know you've arrived safely.
—I won't forget.Goodbye then.
—________.[ ]
A. With pleasure
B. Have a nice trip
C. Don't mention it
D. It's very nice of you
煤尘爆炸的上限浓度一般为（）。
A、300~400g/m3
B、1500~2000g/m3
C、大于2000g/m3
