20 12 03 15 the central meteorological observatory released the weather forecast for Yinchuan and Hainan in the next 24 hours: Yinchuan, sunny, with a temperature of 3℃∽- 10℃.

Hainan is surrounded by the sea, with plenty of water and large specific heat capacity. During the day, compared with the quality of water and gravel, the absorbed heat is the same, and the temperature of water rises less.

The same heat is released at night, and the water temperature drops less, which makes the temperature difference between day and night in Hainan small; However, the soil in Yinchuan inland area is sandy, with small specific heat capacity and large temperature difference between day and night.

So choose B.