You are presented with the quiz "what is fan speed?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "the vanes rotating in an electric fan causes air to move" and "output of the fan is varied by means of a series of adjustable vanes upstream of the impeller". So, what's the best answer to the question?
Choices:
-- energy barrier.
-- kinetic energy.
-- fixed.
-- cycles.
-- Winter.
-- static.
-- solid.
-- adjustable.
adjustable