Which of the following equations corresponds to the definition of enthalpy of formation at $298 \ K$?

• A
  $C(graphite) + 2H_{2(g)} + \frac{1}{2}O_{2(g)} \to CH_3OH_{(g)}$
• B
  $C(diamond) + 2H_{2(g)} + \frac{1}{2}O_{2(g)} \to CH_3OH_{(g)}$
• C
  $2C(graphite) + 4H_{2(g)} + O_{2(g)} \to 2CH_3OH_{(l)}$
• D
  $C(graphite) + 2H_{2(g)} + \frac{1}{2}O_{2(g)} \to CH_3OH_{(l)}$