Answer:
Option 3: to show the effect of the black hole’s gravity
Step-by-step explanation:
This is the answer because option 1 "to reveal the color of a black hole" is very stupid as a black hole in space is invisible because well it's dark ad space is pitch black as well (unless you count the stars). Option 2 is also dumb because it being appealing is not a good trait for something that swallows things up and almost NEVER brings them back up. Option 4 is the dumbest of all "to show that it is cold around a black hole" we already know that it's cold, IT WOULDN'T BE IN SPACE!!!!!!!!! But, it also has stars inside of it and sometimes it actually spits dust out of it, and blue is NOT it's main color.
I hope this helped stay safe and happy!! ;)