What Best Explains Why a Desert Is Cold at Night

What best explains why a desert is cold at night? 

A)  because the relative humidity of the desert is very high, making the air feel cold 
B)  because there is little vegetation and moisture to help store the heat, and the skies are usually clear 
C)  because nights in the desert are very cloudy and block lunar radiation 
D)  because winds in the desert originate at the north and south poles