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e) To gauge optimism and pessimism, the researchers set up an experiment involving 22 calves.

a) Before they started the experiment, they trained the calves to understand which of their choices would lead to a reward.

d) In the training, each calf entered a small pen and found a wall with five holes arranged in a horizontal line, two-and-a-half feet apart.

c) The hole at one end contained milk from a bottle, while the hole at the opposite end contained only an empty bottle and delivered a puff of air in calves' faces.

b) The calves learned quickly which side of the pen held the milk reward.