Answer:
The conditioned stimulus is the song
Step-by-step explanation:
Maceo hated having his diaper changed but he loved cake. So, Maceo's father decided to use classical conditioning to make diaper changes less miserable. Every time he changed Maceo's diaper, he would play the same song and give Maceo a small bite of cake. Now, as soon as Maceo hears the song, he is happy to have the diaper changed. The conditioned stimulus is the song.