How long has the man suffered from the symptoms he described?

Listen to the conversation， mark each question as A， B， C or D according to your listening.
M: Good morning， Doctor.
W: Good morning， Mr. Smith. What can I do for you?
M: I feel there’s something wrong with me， but I’m not sure.
W: Could you explain more to me?
M: I got a runny nose， watery eyes， sore throat and other symptoms on Monday and they last the following five days. Since I’m terribly busy with my work， I won’t have time to see the doctor. But when I do have time to see the doctor on weekends， the symptoms will disappear suddenly!
W: And you will get the same symptoms again the next Monday?
M: Exactly.
W: How long have you been like this?
M: About one month.
W: Did anything special happen during the past four weeks?
M: Nothing special. Oh， wait! My company has moved into a new building.
W: That’s it. When a new building is just finished， the chemical vapors of paint can’t escape the building， so people can’t breathe properly. So they get sick.
M: Well， I got the reason. Thank you， Doctor.