Stars Begin as Nebulae

Steps:

• Recall the stellar life cycle starts with gravitational collapse of interstellar material.
• Identify the initial material as diffuse clouds in space.
• Recognize that these clouds are primarily hydrogen and helium gas mixed with dust.
• Confirm the first stage is before nuclear fusion ignites in a protostar.

Why B is correct:

• By definition, the stellar life cycle begins with a nebula, a cloud of gas and dust that collapses under gravity to form protostars, as per the nebular hypothesis.

Why the others are wrong:

• A: Black holes form at the end of massive stars' lives after supernova collapse.
• C: Red supergiants are late evolutionary stages for massive stars before exploding.
• D: Supernovae are explosive deaths of massive stars, not the beginning.

Final answer: B