Question

which factor causes gas and dust to pull together during the first stage of star formation?
density
gravity
heat
pressure

Explanation:

Gravity is the force that attracts matter. In star formation, gravity pulls gas and dust together. Density is mass per unit volume. Heat is thermal energy. Pressure is force per unit area. But it is gravity that initiates the pulling - together process in the first stage of star formation.

Answer:

B. gravity