oxidize chemicals to obtain energy

Question

obtain energy from light and carbon from carbon dioxide

use light energy to synthesize water and sugar

obtain electrons from oxygen and carbon from organic molecules

WHICH ONE DO WOULD YOU PICK. I AM CLUELESS.

This site is LONG and LONGER but don't give up. Scroll down and near the end they talk about photoautotrophs, and other kinds of "trophs" and define the term. Your answer is there. In the process, you can learn about microbiology, microbes, and other neat things.
http://www.theguardians.com/Microbiology/gm_mbi01.htm