Which of the Following Experiments Involves the Use of Operant

Which of the following experiments involves the use of operant conditioning?

A) blindfolding someone and timing him to see how long it takes him to estimate the size of a room
B) determining how long it takes someone to learn how to fish if he is only allowed to watch other people fishing
C) pairing a puff of air to the eye with seeing the color red in order to find out how many repetitions it will take for someone to blink when he sees the color red
D) rewarding a child for finishing his oatmeal mush and counting how many times the child needs to be rewarded before he finishes his oatmeal voluntarily