How did cats in Thorndike's puzzle boxes typically behave?

A) At first they struggled to get out, but once they got out successfully they were able to get out very quickly on the next try.
B) They were let out of the box after they produced the required amount of saliva.
C) They were frustrated at first, but eventually experienced learned helplessness and gave up.
D) They learned gradually, through trial and error.

Thorndike's puzzle boxes were used to study animal learning through trial and error. Cats were placed in the boxes and had to figure out how to press a lever or pull a string to open the door and escape. Initially, they would struggle and make random movements, but over time they would gradually learn through their mistakes and eventually succeed in opening the door. This process of learning through trial and error became known as the "law of effect," which states that behavior that is followed by a positive consequence is more likely to be repeated in the future. Therefore, option D, "They learned gradually, through trial and error," is the best choice.