What is the relationship between the apparent brightness of any light source and the distance from the light source to the observer?

A、The apparent brightness is proportional to the distance from the light source to the observer.;
B、The apparent brightness is proportional to the square of the distance from the light source to the observer.;
C、The apparent brightness is inversely proportional to the distance from the light source to the observer.;
D、The apparent brightness is inversely proportional to the square of the distance from the light source to the observer.