the star remains in this stage for billions of years\nmain sequence\nblack hole\nred giant\nsupernova\nneutro…

Brief Explanations:

Stars spend the majority of their lives in the main - sequence stage. During this stage, they fuse hydrogen into helium in their cores, and this stable energy - producing process can last for billions of years. A black hole is the remnant of a massive star after a supernova explosion (for very massive stars), and it is not a long - lasting stage like the main sequence in terms of the star's "active" life (in terms of energy production like fusion). A red giant is a late - stage of a star's life when it has exhausted hydrogen in its core and is expanding, and it does not last as long as the main sequence. A supernova is a short - lived explosive event. A neutron star is also a remnant (for stars of a certain mass range after supernova), not a long - lasting stage like the main sequence. A nebula is a cloud of gas and dust, often a birthplace or a result of a star's death (planetary nebula), not a stage where a star remains for billions of years in an active sense. A white dwarf is the end - stage of a low - to medium - mass star after it has shed its outer layers, and it cools over time but is not a stage with active fusion (like the main sequence) for billions of years. A protostar is in the early formation stage, not a long - lasting stage for billions of years with stable energy production like the main sequence.

Answer:

Main sequence