Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to reestablish an equilibrium.

For the backward reaction to be favoured(LHS) , the concentration of one of the reactants must be reduced. i.e either E or F must be reduced. However, from the option, option C happens to be the one that fits in, as E is the only reactant reduced.