The star in the life cycle that fuses hydrogen and helium is a main sequence star.

Here's why:

* Main sequence stars are the most common type of star. They are in a stable stage where they fuse hydrogen into helium in their core. This process releases energy that makes the star shine.

* Hydrogen fusion is the primary energy source for main sequence stars. It's the process that powers the star for the majority of its lifetime.

So, while other stages of a star's life involve different fusion processes, it's the main sequence phase where hydrogen-helium fusion dominates.