In September 1 (1), Xiao Ming said: If I don't know, Xiao Qiang certainly doesn't know. It can be inferred that M=3 or 9. Because when M=6 or 12, N=7 or 2 may appear, that is, June 7th or 65438+February 2nd, so Xiao Qiang can immediately know that this is not in line with Xiao Ming's inference. When M=3 or 9, N= 1 or 4 or 5 or 8, these are all repetitions, which Xiao Qiang certainly doesn't know. At this time, in addition to June and 65438+February, there are four dates to choose from, namely March 4th, March 5th, March 8th, September 1 day and September 5th (2) Xiao Qiang said: I didn't know at first, but now I know. According to Xiao Ming's first inference, Xiao Qiang knew the date as soon as he knew M=3 or 9, so he could rule out N=5. March 5 and September 5 cannot be chosen immediately. At this time, the dates to be selected are still March 4th, March 8th and September 1 day (3). Xiao Ming said: Oh, I know. Xiao Ming also inferred from Xiao Qiang's words that n was not the answer chosen after 5. You can know that teacher Zhang's birthday is September 1. Because when M=3, there are two options in March, and Xiao Mingcan can't choose the correct answer; When M=9, I know the correct answer without choosing.