Which event takes place first in the stages before the birth of a star? Gravity pulls gas and dust together. A protostar forms as mass increases. Nuclear fusion begins under high pressure. A protostar collapses and becomes denser.

Gravity pulls gas and dust together.

Explanation:

nebula (as the first stage is called) : the first stage before the birth of star is seen by a slow rotating, clouds of cold gas and dust. the nebula condenses into a huge globule of gas and dust which shrink under its own gravity

(A) Gravity pulls gas and dust together.