What Makes a Gas Cloud Contract to Form Stars

What makes a gas cloud contract to form stars?

A) The cloud's magnetic field draws material together.
B) The dust in the cloud is pulled together by static electricity.
C) All parts of the cloud are gravitationally attracted to all other parts, collapsing the cloud.
D) Pressure from meteor collisions pushes the cloud together.
E) Uranium atoms attract lead atoms by nuclear fusion.