At its peak, the Aztec empire controlled * A. all of present-day Mexico. B. an area extending from central Mexico to Guatemala.
C. several isolated cities in the forests of Central America.
D. a vast region connected by roads in the Andes.

taxation that is paid in kind, that is with goods or services rather than money

in classical conditioning the organism learns to associate new stimuli with natural, biological responses such as salivation or fear. the organism does not learn something new but rather begins to perform in an existing behavior in the presence of a new signal. operant conditioning, on the other hand, is learning that occurs based on the consequences of behavior and can involve the learning of new actions.