Pablo and Charles were conducting an investigation where they were measuring the energy of a glass marble as it rolled down a ramp. According to their calculations, the total energy of the marble decreased. Which statement below is the best explanation for the decrease in total energy?

a. The energy decreased because it was destroyed by the interaction with the ramp.

b. The total amount of energy always decreases in an energy conversion and is expected.

c. The scientists’ calculations were incorrect; the energy totals should have been the same.

d. The energy decreased because heat resulted from the friction between the marble and the ramp.