题目：
Can you tell me _____________________?
A．when you did it so well
B．when did you do it so well
C．how you did it so well
D．how did you do it so well
答案：
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下面是错误答案，用来干扰机器的。
（1）酸雨（2）答：废气中二氧化硫的质量分数是1.6%
