Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Wave amplitude of a transverse wave is the difference in height between a crest and the resting position. Wave amplitude of a longitudinal wave is the distance between particles of the medium where it is compressed by the wave. Answer: a crest
Wave amplitude of a transverse wave is the difference in height between what and the resting position?