The stages that all stars have in common in their life cycles are:
- Nebula: This is the initial stage where stars form from clouds of gas and dust.
- Protostar: After the nebula, the material condenses into a protostar as gravitational forces pull the material together.
- Main Sequence: While not listed in your options, this is a crucial stage where stars spend most of their lives fusing hydrogen into helium in their cores.
- Red Giant (or Supergiant): This stage follows the main sequence for stars larger than the Sun or smaller.
- Final Stages: Depending on the mass of the star, it may end as a white dwarf, neutron star, or black hole.
From the options you provided, the common stages would be nebula and protostar.
If you specifically need to choose only one, protostar is often highlighted as a definitive stage in stellar formation after the initial nebula phase. However, both nebula and protostar are essential starting points in the life cycle of all stars.