To analyze a variable we must have some parameters that must be constant in the experiments, in this case, we would have two parameters, the concentration of HCl and the temperature of the HCl, if we want these two parameters not to affect our measurements, they must be constant when varying the particle size that will be our variable to study.
Now we have according to the table two options in which we change the particle size but the other parameters remain constant. They will be experiments A and B and experiments D and E.
Since only option A and B is available, this will be the correct answer.