In the unbalanced oxidation-reduction reaction CH₄ + O2 → CO₂ + H₂O, which answer choice below shows the correct, balanced half-reaction for oxygen?
1) O2 → 2O-
2) O2 → 2O²⁻
3) O2 + 4e- → 2O²⁻
4) O2 + 2e⁻ → 2O-