In a forward reaction which means that the reactants directly form the product, and no possibility of the backward reaction occurring, three of the given choices would likely increase the rate of reaction. First, (a) increasing the temperature. This would increase the kinetic energy in the system, allowing more contact between the molecules. Also (c) removing the inhibitor. This is likely to remove the unwanted compounds in the reaction. Thus, promoting the forward reaction. Lastly, (d) adding a catalyst. Although the compound does not participate in the reaction, it lowers the required energy for the reaction to occur.
With those stated above, the answer to this item would have to be letter b. Lowering the concentration of the reactants.