over the summer break, jed earns extra cash working as a salesman at sensational sound systems. as one of the most knowledgeable salesmen on staff, jed tells a young couple shopping for a sound system that the more expensive models are worth the money because they

a. amplify sound up to 160 db
b. filter out frequencies below 1 hz
c. boost frequencies below 80 hz
d. buffer sounds that reach 60 db