Can someone help me? I probably know the answer but I'm having a brain fart.

Answer:
I beleive the answer is a.
Explanation:
This is because a star is the smallest and a universe is the largest. So this only leaves two in the middle, star system and galaxy. We know a star system is made up of stars, so it would come after star. The galaxy after that because it is smaller than a universe and star systems are in a galaxy.
Hope this helps and if possible brainliest??