题目

I used to believe courtesy was a thing of the past. Very seldom have I encountered a courteous human being in this modern era. Recently, I had to change my thinking, when I came face to face with just such a human being in a coffee place, with my two daughters. The place was crowded as usual and we had to climb steep(陡峭)stairs in order to find an empty table. After enjoying coffee and snacks, we went down the narrow stairs, where there was hardly any space for another person to either climb up or come down. Just as I was in the middle of the stairs, a gentleman entered the main ent已知整数按如下规律排成一列：（1，1），（1，2），（2，1），（1，3），（2，2），（3，1），（1，4），（2，3），（3，2），（4，1），…，则第30个数对是（2，7）（2，7）．