For the hypothetical reaction $2X + G \to Q + 2M$,the rate expression is $\frac{d[Q]}{dt} = k[X]^2$. Which of the following is the most likely mechanism?

• A
  $2X + G \rightleftharpoons 2Q + R$ (fast)
  $Q + R + G \to 2M$ (slow)
• B
  $X + G \rightleftharpoons Q + R$ (fast)
  $R + X \to 2M$ (slow)
• C
  $X + X \rightleftharpoons X_2$ (fast)
  $X_2 \to Q + T$ (slow)
  $T + G \to 2M$ (fast)
• D
  $G + G \rightleftharpoons G_2$ (fast)
  $G_2 + X \to Q + T$ (slow)
  $T + X \to 2M$ (fast)