Thorndike's Research with Cats in Puzzle Boxes Led Him to Conclude

Thorndike's research with cats in puzzle boxes led him to conclude that

A) cats learn by insight and can grasp the nature of a problem.
B) we all experience an "aha reaction" where we solve a problem and respond correctly after that point.
C) all learning, in animals and humans, occurs by trial and error.
D) learning that is strongly reinforced occurs faster and is less subject to extinction.