Answer: planetary accretion
Explanation: Astronomers think planets formed from interstellar dust and gases that clumped together in a process called planetary accretion. The correct option among all the options given is the planetary accretion. Basically this process is when particles of metal and rock come together and grow into a full planet. However, the word accretion actually means the formation of planets and other bodies that are created by the materials collected due to gravitational force.
