Adding a catalyst to a reaction has an effect similar to
a. decreasing pressure.
b. increasing temperature.
c. adding water to a reaction.
d. lowering the concentration.

The answer is B. Increasing temperature.

Explanation:

The role of a catalyst is to facilitate the occurrence of a reaction, trough differents methods (by lowering the activation energy for example). Its indirectly means that there will be more molecules of reactants that interact between them to produce a given product.

When you increase the temperature, the effect is similar and this is because it causes an increment in kinetic energy of molecules of reactants that collides more and interact to form the product.

When there is a decrease in pressure, distance between  reactant´s molecules will be greater and less number of interaction occur. Something similar occur when you add water, you dilute the concentration of reactants and the distance between its molecules will increase. Lowering the concentration will have the same effect.