单项选择题

Conversation 1
[听力原文]6-7
M: I went to Professor Smith’s office to turn in my paper yesterday, but I found the door was locked.
W: Why did you go there yesterday It was Saturday.
M: Well, you told me to hand it in on Saturday.
W: I said nothing of the sort. What I actually said was you had to turn in your paper by Friday.
M: Oh, really That’s too bad. Professor Smith will be mad at me since I have been late in turning in my homework for a few times this term already.
W: Oh, he will understand. It’s not easy for you to study and work part time as well. But you do need to give him an apology.
M: Yes, I’ll do that.

When did the man go to the professor’s office to turn in his paper（）

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