Question

two critical requirements must be met before light elements, like hydrogen or helium, will fuse and form heavier elements. the two requirements of nuclear fusion are
a high energy and low density
b extreme temperatures and low density
c extremely high temperature and density
d strong gravitational forces and high density

Explanation:

Nuclear fusion requires extremely high temperatures to overcome the electrostatic repulsion between positively - charged atomic nuclei and high density to increase the probability of nuclear collisions.

Answer:

C. extremely high temperature and density