In Harlow's study with monkeys manipulating puzzles, the reward was:

A) food
B) water
C) opportunity to socialize with other monkeys
D) opportunity to manipulate the puzzles

In Harlow's study, the reward for the monkeys manipulating puzzles was the intrinsic satisfaction or pleasure they derived from solving the puzzles themselves, not an external reward like food, water, or socialization. This finding was significant in demonstrating that the motivation to learn could be driven by curiosity and the intrinsic pleasure of solving problems, rather than by external rewards.