Final answer:
Gas Giants did not become stars because they lack the necessary mass to create the central pressures and temperatures needed for nuclear fusion. Factors such as composition and location beyond the frost line do not inhibit star formation.
Step-by-step explanation:
The reason the Gas Giants did not form into stars is C) Gas Giants are not massive enough to generate fusion. In the process of star formation, a large enough concentration of hydrogen must collapse under gravity to reach densities and temperatures high enough to initiate nuclear fusion. This reaction transforms hydrogen into helium, releasing tremendous energy that powers the star. The Giant Planets in our solar system, despite being composed primarily of hydrogen and helium and having considerable mass, failed to accumulate the necessary mass—typically tens or hundreds of times that of Jupiter—to reach the central temperatures and pressures required for fusion.
It's also worth noting that, while Gas Giants indeed contain helium and are found beyond the frost line, neither of these factors prevent star formation. Helium is actually a product of fusion in stars, and the frost line's distance from a star relates more to planetary formation than the birth of stars.