Question

two sound waves from different sources intersect and the volume of the sound becomes louder.
when a person yells out over a canyon, they hear an echo of their voice.
choose
choose
diffraction
interference
refraction
reflection

Explanation:

For the first scenario (Two sound waves... louder):

When two sound waves intersect and the sound becomes louder, this is constructive interference (a type of interference) where waves add up. Diffraction is bending, refraction is bending at a boundary, reflection is bouncing. So the correct term is Interference.

An echo is caused by sound waves bouncing off a surface (the canyon walls), which is reflection. Diffraction is spreading, interference is wave interaction, refraction is bending. So the correct term is Reflection.

Answer:

Interference

For the second scenario (Person yells over canyon... echo):