The solar system formed from the

A. collapse of an interstellar cloud.

B. explosion of an interstellar sun

C. grouping together of asteroids

D. collision of two massive stars

The correct answer is A. collapse is an interstellar cloud. This happened around 4.6 billion years ago and it resulted in what's nowadays known as the solar system, out of which the largest mass is owned by the Sun itself. There are 8 planets, and 5 dwarf planets, with Pluto who was a regular planet joining them recently.