<image>Look at the picture and fill in the blanks.
(1) The temperature difference between the two cities is the smallest in ____ month, and the largest in ____ month ____________________.
(2) The average temperature in ____ city in ____ month drops the fastest compared to the previous month.
(3) The average temperature over these four months in Nanjing is ____, the average temperature over these four months in Harbin is ____, and the difference in average temperature between these two cities is ____.