The four astronomical bodies represents here are A represents Universe, B represents Galaxy, C represents Solar System, and D represents Mars.
The hierarchical level D is different from the rest is because Mars is a planet and unlike all other astronomical bodies it does not hold other astronomical bodies with in it.
What are astronomical bodies?
"Astronomical bodies are objects in space like sun, moon, planets, and stars. They form a part of the vast universe we live in and are very far from Earth."
What is Universe?
"The universe includes all space, time, and their objects that also includes planets, stars, galaxies, and other forms of matter and energy."
What is Galaxy?
"Galaxy is a vast collection of dust, gas, billions of stars with their solar systems that are all held together by gravity."
What is Solar System?
"Solar System is a gravitationally bound system of eight planets, their moons in orbit round the sun with small bodies like comets, meteoroids, and asteroids."
What is Mars?
"Mars is the fourth planet from the sun and the second smallest planet in the Solar System."
To learn more about Mars and Solar System here
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