The EM spectrum has no limits. Any frequency you can imagine
is the frequency of some electromagnetic radiation somewhere.
The Law of the Conservation of Energy is stating that the total mechanical energy is always conserved or in simpler terms, not used or saved.
The correct answer would be D. A new experiment would be needed to be done in order to test the conclusions. In science there is no authority, data is the only thing that matters. So if we have two different conclusions from the same date the only solution is to perform more tests and more experiments to see what is correct.
Any one trial might have been done incorrectly.