Hi,

This can be tricky, but recall that the MCAT wants you to select the best answer, and some answers can be partially correct.

If you think about water, it is not a large molecule - but because you can absorb heat from breaking H bonds - which allows you to absorb a lot of energy without increasing the average kinetic energy of particles and thereby the temperature of the sample.

The reason you would pick D over A is because D is an answer that is true in all cases - as heat capacity is the amount of energy a substance per the increase in temperature - there need to be other outlets for the energy.

A doesn't address this concept - so although it is correct, it doesn't get to the heart of the matter of what heat capacity is.

I understand that this is a bit unsatisfying as an answer, but it is this type of question that makes the MCAT quite tough as a test.

Please let me know if you need more clarification.