A's birthday is in early March, and B's birthday is in late April, both of which are on Thursdays. If the sum of their birthdays is 33, what day is A's birthday in March?
甲的生日在3月上旬，乙的生日在4月下旬，并且都是星期四，如果两人生日的日期数的和是33，那么甲的生日是3月多少日．
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