问题
Every year there are about _______ people waiting for their trains back home in the railway station before Spring Festival comes.
A:when you did so well
B:when did you do it so well
C:how you did so well
D:how did you do it so well;
B:when did you do it so well
C:how you did so well
D:how did you do it so well;
正确答案是：
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