The DIRECTION of a reversible reaction can be changed by. __ adding a CATALYST [BOTH of these] [NEITHER of these] altering the CONDITIONS

# Explanation:## Step 1:A reversible reaction is one where the reactants can form products, which can then revert back to reactants. The direction of such a reaction can be influenced by various factors.## Step 2:A catalyst speeds up both the forward and reverse reactions equally without favoring one direction over the other. Therefore, it does not change the direction of the reaction.## Step 3:Altering the conditions, such as temperature, pressure, and concentration, can shift the equilibrium position of a reversible reaction. For example, according to Le Chatelier's principle, increasing the temperature of an exothermic reaction will shift the equilibrium to favor the reactants.## Step 4:Thus, altering the conditions can change the direction of a reversible reaction, while adding a catalyst cannot.# Answer: altering the CONDITIONS