The correct sequence in the life cycle of a massive star is:
**nebula, protostar, star, super red giant, supernova, neutron star**
This sequence outlines the general progression through which a massive star evolves from its initial formation to its final stages. Here's a brief explanation of each step:
1. **Nebula**: A cloud of gas and dust in space where stars begin to form.
2. **Protostar**: A stage where the nebula collapses under gravity and starts to form a dense core.
3. **Star**: The protostar continues to accumulate mass and eventually ignites nuclear fusion in its core, becoming a main-sequence star.
4. **Super Red Giant**: As the star exhausts its hydrogen fuel, it expands and cools to become a super red giant.
5. **Supernova**: The massive star culminates in a supernova explosion, often at the end of its life cycle.
6. **Neutron Star**: The remnant core left after a supernova can become a neutron star if it is below a certain mass threshold.
So, the correct choice is:
**nebula, protostar, star, super red giant, supernova, neutron star**.