Weather is the main factor.

Shanghai and Macao belong to coastal areas, where there is much water and the specific heat capacity of water is large. Shijiazhuang and Urumqi belong to inland areas, with sandy soil as the main surface and small specific heat capacity of sandy soil.

During the day, compared with land, water with the same quality absorbs the same heat, and the temperature of water rises less, while the temperature of sandy soil rises more; At night, when the same amount of heat is released, the temperature of water drops less and the temperature of sand and gravel soil drops much, so the temperature difference in inland areas is larger than that in coastal areas.

So choose C.