:astronomers think planets formed from interstellar dust and gases that clumped together in a process called 1.)stellar evolution 2.)nebular aggregation 3.)planetary accretion 4.)nuclear fusion

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 in the question is option "3". The word accretion actually means the formation of planets and other bodies that are created by the materials collected due to gravitational force. 

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Astronomers think planets formed from interstellar dust and gases that clumped together in a process called planetary accretion. Basically this process is when particles of metal and rock come together and grow into a full planet. The correct choice is

3. planetary accretion

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