Which is a perfectly balanced equation with no excess leftovers that uses exactly 4 CH₄ molecules:
a) 4 CH₄ → 4 C + 8 H₂
b) CH₄ + O₂ → CO₂ + 2 H₂O
c) CH₄ + 4 Cl2 → CCl₄ + 4 HCl
d) 2 CH₄ + 3 O₂ → 2 CO + 4 H₂O