The answer is letter a. Hill terrain, hill slope, and hill elevation
In a high-mass star, hydrogen fusion occurs via the CNO (Carbon-Nitrogen-Oxygen) cycle.
According to the life cycle of a star, there are three main phases in the life of a star: The initial phase (a quick phase), short phase or supergiant phase and death phase or supernova explosion.
the CNO cycle means Carbon-Nitrogen-Oxygen cycle and this process tale place during main sequence phase.
In this phase, hydrogen fuses into helium as a result of six different reaction taking place inside a star.
The first step of the sequence begins when the nucleus of carbon 12 isotope emits gamma rays after capturing a proton and produces nitrogen-13.
This whole cycle is known as stellar nucleosynthesis.
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