The answer you're looking for is D. If you're misrepresenting scientific knowledge, in order to get the people on board and to agree with it, then people begin to find out and then you lose their trust.
Star brightness is defined by either D. apparent magnitude - when we measure it from Earth (that is how bright it is from Earth) - this is the closest to "basic observation" and the best answer
or by absolute magnitute - how bright it would be at a certain distance (this allows to compare the brightness).