Which of the Following Are Combination Reactions? 1) CH₄ (G)

Which of the following are combination reactions? 1) CH₄ (g) + O₂ (g) → CO₂ (g) + H₂O (l)
2) CaO (s) + CO₂ (g) → CaCO₃ (s)
3) Mg (s) + O₂ (g) → MgO (s)
4) PbCO₃ (s) → PbO (s) + CO₂ (g)

A) 1, 2, and 3
B) 2 and 3
C) 1, 2, 3, and 4
D) 4 only
E) 2, 3, and 4