Question

In which part of the wave are the particles of the medium closer together?

Answer 1

B.compressions

Explanation:

This is a characteristics of the "longitudinal waves".

Longitudinal waves are waves where the oscillation of the particles of the medium occurs in a direction parallel to the direction of propagation of the wave (an example of longitudinal waves are sound waves). As a consequence, this oscillation creates some regions where particles are closer together, and other regions where particles are more spread apart. The former are called "compressions", while the latter are called "rarefactions".

Answer 2

B.) Compressions 
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