Andrea is the mother of Leo, a six-month-old child. She wants to introduce vegetables in Leo's diet. As Leo is used to having lentil soup as his evening snack, Andrea prepares lentil soup with vegetables in it and makes Leo taste it. He does not like the taste of the soup and refuses to have it. After that day, he refuses to have even plain lentil soup. In this scenario, which of the following acts as the conditioned stimulus? a. Andrea
b. Leo
c. the vegetables
d. the soup