The conversion between different states of energy (e.g. potential energy to kinetic energy)

A) is not 100% efficient.
B) is 100% efficient.
C) typically generates heat.
D) is not possible; energy cannot change its state.
E) is not 100% efficient and typically generates heat.

The conversion between different states of energy is not 100% efficient due to the second law of thermodynamics, which implies that some energy is always lost as heat during the conversion process. This makes option E correct, as it combines both the inefficiency of energy conversion and the generation of heat, which are common characteristics of energy transformations.