Problem: Given the question: M: Why don't we go by bike? It's faster. What was said before this conversation?
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The answer is:
W: Shall we go to the zoo on foot?

Problem: Given the question: W: But I tell you I didn't take it. I remember clearly that you put it on the dressing table. What was said before this conversation?
++++++++++++++++++++++++++++++++
The answer is:
M: You must have left the camera in the market. It's a very good camera you know, Sandie.

Problem: Given the question: M: I arrived here an hour ago. What was said before this conversation?
++++++++++++++++++++++++++++++++
The answer is:
W: Excuse me, when did you arrive here, Mr. Wang?