Task: Question Answering
Input (English): An unbalanced equation for the reaction of methane gas (CH_{4}) with oxygen is shown below. CH_{4} + \Box O_{2} -> 2CO_{2} + 4H_{2}O How many molecules of oxygen gas (O_{2}) are needed to properly balance this equation?  
 (A) 1 (B) 2 (C) 3 (D) 4
Output (English): D