lol, wierd, i think its cuz- not all energy is transformed to k.e, i dont think this goes like tht law of cnservation of falling bodies (where at falling ,some of it is ke and some of it is pe.)
cuz the question says "the energy transoformations" and the mark scheme avoids by saying tht the whole pe was changed to something, as it only said transformed or decreased...
and heat is a must, as heat is lost due to friction, as any waste enrgy is lost mostly by heat.