Part 1 Answer
A: Universe
B: Milky Way
C: Clusters
D: Planets
Part 2 Answer
The universe is the entire cosmic spectrum of all matter and all things. It includes everything else -- galaxies, star clusters, stars, planets. Therefore, it's A.
The Milky Way is a galaxy -- a system of stars and interstellar matter. Therefore, it is B, because it contains all of the below.
Inside the galaxy are C and D.
C is the cluster: an assembly of stars held together by the mutual gravity of everything inside.
And inside the cluster will be D: any planets that are also inside clusters, which also reside in a Galaxy, which resides inside the universe.
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Feel free to comment any questions you have. I have used britannica.com as a source for these terms.