Which sequence correctly represents the life cycle of a massive star starting from a nebula?

• A. Nebula -> Big Star -> Red Supergiant -> Supernova
• B. Nebula -> Protoplanetary Disk -> Young Star -> Main Sequence
• C. Nebula -> White Dwarf -> Planetary Nebula -> Black Hole
• D. Nebula -> Neutron Star -> Black Hole -> Singularity

Answer: (A)

Massive stars begin life in a nebula, a cloud of gas and dust that collapses under gravity to form a hot, bright star. As they burn through their fuel, they swell into a red supergiant, a stage where the outer layers expand while fusion continues in the core. Eventually the core collapses in a core‑collapse supernova, blasting the outer layers into space and leaving behind a dense remnant such as a neutron star or black hole. So the sequence Nebula → big star → red supergiant → supernova captures that progression: birth in a nebula, growth into a massive main‑sequence star, expansion into a red supergiant, and explosive end.

Other options mix in formation stages like a protoplanetary disk or describe end states of lower‑mass stars (white dwarfs, planetary nebulae), which aren’t part of the life cycle of the most massive stars. A line that includes a neutron star or black hole as separate, successive stages is possible after a supernova, but the additional steps aren’t part of the standard path, making the chosen sequence the best fit.