Question

theaters and concert halls often place curtains on the walls in order to _____.
raise the intensity of sound.
increase sound reflection.
prevent refraction
absorb the energy of sound waves

Explanation:

Curtains are soft materials. Soft materials are good at absorbing sound energy rather than reflecting or increasing sound intensity. Refraction is related to the change of sound - wave direction when passing through different media and is not related to curtains.

Answer:

absorb the energy of sound waves