Answer:
b. vibration
Explanation:
Sound is all about vibrations.
The source of a sound vibrates, bumping into nearby air molecules which in turn bump into their neighbours, and so forth. This results in a wave of vibrations travelling through the air to the eardrum, which in turn also vibrates. What the sound wave will sound like when it reaches the ear depends on a number of things such as the medium it travels through and the strength of the initial vibration.
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