During the formation of a star, the contraction stops once
select one:
a. hydrogen fusion becomes the dominant energy source.
b. the star collapses into a black hole.
c. the star collapses into a white dwarf.
d. helium fusion becomes the dominant energy source.

The correct option is option a. hydrogen fusion becomes the dominant energy source.

Explanation:

Options b and c are things that happen to a star when it is nearing its end of life, being becoming a black hole or a white dwarf the final destiny of the star.

Option d happens at the maturity of the star, when enough helium accumulates (from hydrogen fusion) in its core in order to start fusing.

Option a is correct because when hydrogen fusion becomes the dominant energy source the star stops contracting due to inward pressure from gravitational collapse (which allows the initial concentration of mass that forms a proto star) starts being in equilibrium with the outward thermal pressure due to the energy liberated in form of heat by the fusion of hydrogen in the core.

question

which are human systems?

the amazon rain forest

the appalachian trail

the george washington bridge

the himalayas

the hoover dam

the north american free trade agreement