Mary: What are you gonna do today?
Nack: I have music lessons this evening.
Mary: Oh. You teach music?
Nack: Yes. I teach playing guitar.
Mary: Good. Can you play guitar?
Nack: Of course, yes. I can play guitar.
Mary: When did you start to play guitar?
Nack: It was about 20 years ago.
Mary: Were you a student?
Nack: Yes, I was. I was a high school student at that thime.
I was a high school student at that time.