The solar system formed from the a. grouping together of asteroids. b. explosion of an interstellar sun. c. collision of two massive stars. d. collapse of an interstellar cloud.

D. collapse of an interstellar cloud.

Explanation:
The formation of the solar system was explained based on the  Nebular Hypothesis. This hypothesis states that the explosion of the supernova resulted in the disturbance of a cloud of gas and dust in space which led to the formation of the solar system.

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are called Compounds