In this question, we need to determine which option can speed up the rate of a chemical reaction, and there are a few ways possible in order to speed up a reaction, usually we have: Increasing temperature, increasing surface area, increasing the concentration of reactants
In this case, increasing temperature would not make the reaction occur faster, since the reaction is exothermic, therefore there is no need to input energy for the reaction to occur
Increasing the concentration of reactants, is the option A, but there is a small problem, A is a solid compound and B is an aqueous compound, if we add more A, we can speed up the reaction but we can also turn the extra amount of A insoluble, which would not make the reaction to occur faster
The best way, in this case, is to crush reactant A into powder, because this would make the surface area of A to increase, making A and B interact more and then the reaction would occur faster
The best option will be letter C