一个英语补全对话A：Hi,Mandy.You look so worried.（ ）?B：Our teacher asks us to make a poster about“Big Problems in the World”.（ ）.A：Oh,don’t worry.I have heard that population is a big
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What happened?
But I don't know how to do it.
Why not discuss this problem?
Have you searched relevant information?
Fortunately,it haven't been the fact.