Answer:
A. Adding D
Step-by-step explanation:
Based on Le Chatelier's principle, a chemical reaction will reach equilibrium when the rate of the forward reaction is equal to the rate of the backwards (reverse) reaction.
Adding more reactants will cause the equilibrium to shift to the right and form more products in order to reach equilibrium again.
While adding more products will shift the equilibrium to the left and form more reactants in order to reach equilibrium again.
In the given question, we need the equilibrium to shift to the left and form more reactants. This means that we will need to add more products.
Therefore, we will need to add either C or D.
Applying this to the choices, we will find that the correct choice is A.
Hope this helps :)