:star: In the day, presence/absence of cloud cover reflect solar radiation back into outer space as well as absorb some solar radiation/allows the solar radiation to reach the earth's surface. Therefore, earth's surface is not/is heated up excessively.
:star: At night, presence/absence of cloud cover prevents/allows heat radiated from the earth's surface from escaping into space, so temperature falls a few/many degrees only.
:star: Thus, the diurnal temperature range is small/large.
:star: For example, Singapore, which located at 1°North, has extensive cloud cover and lower diurnal temperature range. On the other hand, Sahara desert, with no cloud cover, has high diurnal temperature range