Two similar fans are operating in a room. Fan 1 makes a squeaking noise while running. Fan 2 is silent.

Which fan is more energy efficient?

a. Fan 1, because Fan 2 cannot convert energy into sound.
b. Fan 2, because the silence indicates there is no energy transfer going on in the fan.
c. Fan 1, because the noise indicates there is no energy transfer going on in the fan.
d. Fan 2, because Fan 1 converts some energy to sound.