Explains why anyone in the classroom can hear that loud teacher across the hall even though the door is barley cracked open a. reflection b. refraction c. diffraction

Diffraction: 
Diffraction describes how waves bend, or change direction, as they travel around the edges of obstacles. Diffraction occurs in water waves, sound waves, and light waves, but the amount of diffraction depends on the size of the obstacle or opening in relation to the wavelength of the wave.

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .