An unlabeled hierarchical diagram of some astronomical bodies is shown. the labels a, b, c, and d can be used to represent galaxies, solar system, clusters, universe, and planets.

part 1: which four astronomical bodies would you choose to represent the four labels in the diagram?
part 2: justify your choice based on the hierarchical relationships in astronomical bodies.

Part 1
A ->Universe
B ->Galaxies
C ->Solar system
D ->Planets

Part 2
Of all possible choices planets are smallest. That's why they are in a circle D.
Multiple planets and one or more stars form solar system. They are in a circle C.
Multiple solar systems form galaxies. They are in a circle B.
Galaxies are pulled by gravitational forces and together they form clusters.
Universe is biggest possible space. All of the above objects are placed inside universe.