=+5. Students are accustomed to a bell ringing to indicate the end of a class period. The principal decides to substitute popular music for the bell to indicate the end of each class period. Students quickly respond to the music in the same way they did to the bell. In this example, the music is a(n)

a. conditioned response.

b. conditioned stimulus.

c. unconditioned response.

d. unconditioned stimulus.

e. habituated response.