Shandong Meteorological Observatory releases the weather forecast of major cities in our province every day, as shown in the figure, the inland city of Jinan and the coastal city of Qingdao on April 23, 213.

There is more water in coastal areas, and the specific heat capacity of water is larger. During the day, compared with sand and gravel, water with the same quality absorbs the same heat, and the temperature of water rises less.

At night, the same heat is released, and the temperature of water decreases less, which makes the temperature difference between day and night in coastal areas small. From the table, it is known that the temperature difference in city B is small, so city B is Qingdao, and city A is Jinan.

Therefore, the answer is: Jinan; The temperature difference between day and night in coastal areas is small.