What does the shaded area represent?
Short answer: The two curves are the distribution of kinetic energy of molecules at two different temperatures. A catalyst won't change the distribution; only temperature change will change the energy distribution. The line marked Ea is the activation energy; a molecule has to have more than this to react. A catalyst could change the activation energy; since there is only one Ea, we can eliminate catalytic activity as an issue. All the molecules with less energy than this just bounce around, not reacting.

The curve with the higher peak represents the lower temperature. The one with the lower peak has a longer and higher tail out to higher energies, so the shaded area represents the greater number of high energy (reactive) molecules at the higher temperature. Answer: A.