If you have problems with this question, check Chapter VII.1D in the Review 17. Hydrogen will not combine with oxygen at a low temperature. Energy is needed to overcome electrical repulsion of hydrogen nuclei. Electrons will not recombine at low temperatures. The force of gravity is greater at high temperatures.
Speeds are less at high temperature, so there is more time for reactions between nuclei.
If you have problems with this question, check Chapter VIII.1A in the Review 18. Name 2 possible ways to ionize neutral interstellar gas close to the sun. If you have problems with this question, check Chapter IX.2 in the Review 19. We know that the Sun's energy does not result from a chemical burning of coal. There is no ash on the bright surface of the sun.