Darrel Was Dancing with His New Girlfriend at an Elvis

Darrel was dancing with his new girlfriend at an Elvis tribute. When the band started playing, "Can't Help Falling in Love with You," his girlfriend gave him a long, passionate kiss, which Darrel found very enjoyable. Now Darrel finds that every time he hears "Can't Help Falling in Love with You" on the radio, he becomes mildly excited. In this example, the long, passionate kiss is a(n)

A) conditioned stimulus.
B) unconditioned response.
C) conditioned response.
D) unconditioned stimulus.