65438+1October 4th 65438+1October 22nd

March1March 5

July1July 2 July 8

65438+ Exclude October and July first, because

B said, "If I don't know A's birthday, then C certainly doesn't know."

It can be seen that if it is 65438+ 10 or July, then the dates may be 65438+ 10, October 22nd and July 2nd.

At this point, C who knows the date can know A's birthday. (Because 22nd and 2nd don't coincide with other dates)

The remaining optional dates are

1 1.4 1. 1.5 1. 1.8

March1March 5

C said, "I didn't know it before, but now I know it."

Excluding the fifth day, if it is the fifth day, C should still be unable to determine the exact birthday.

So the remaining dates are

165438+1October 4th165438+1October 8th.

March 1

B said, "Oh, I see."

Similarly, excluding 1 1 month, if it is 1 1 month, B should still be unable to determine the exact birthday.

To sum up, it is March 1.