Which Experiment Involves the Use of Classical Conditioning

Which experiment involves the use of classical conditioning?

A) blindfolding someone and timing him to see how long he takes to find a button hidden in a room
B) determining how long it takes a person to learn how to knit if he is only allowed to watch YouTube videos of people knitting
C) knowing that a student fears exams, the instructor wears a bright red shirt only on exam day, every exam day, to see how long it is before the red shirt becomes an object of fear to the student
D) rewarding a boy for finishing his vegetables with ice cream and counting how many nights of reinforcement are required before he voluntarily eats his vegetables