One of the reasons that stars are so large is because

a.) pressure builds to heat the gases
b.) gravity causes expansion
c.) larger masses are easier to heat than small masses
d.) they are composed of hydrogen and helium

Best answer a.) pressure builds to heat the gases

Explanation:

A star is made up a massive  ball of hot gas, large enough that gravity causes it to implode on itself forming a very dense and hot core that then causes nuclear fusion, whereby larger atoms are formed from the combination of much smaller ones, in the process a lot of heat and pressure is generated that then in turn pushes outwards from the core making it larger.

the answers are

c and c

it's 3.2 on edge, i just took the test.