How can studying the historical, cultural, and musical setting of
music add to our enjoyment of it?
A. Studying musical background helps us know
exactly how to compose music.
B. Studying the setting of music is important when
choosing an instrument to play.
C. Knowing the background of a work of music helps
us understand, appreciate, and, therefore, enjoy it.

a

Explanation:

what is the question you are trying to ask here

the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).