Dr. Rubio is conducting an experiment in classical conditioning. Shortly after playing music, she places a loaf of bread on the window sill outside her office window. After doing this a number of times, she notices that now, just as she begins to play her music, several birds fly to her window even before she presents the bread. In this example, what is the conditioned stimulus?

• A. The bread
• B. The sound of the window opening
• C. Dr. Rubio's lab coat
• D. The music