Final answer:
Positive reinforcers strengthen a response by adding a positive stimulus, while negative reinforcers also strengthen a response but by removing a negative stimulus; both aim to increase behavior frequency.
Step-by-step explanation:
Positive reinforcers strengthen a response through the presentation of a positive stimulus; negative reinforcers strengthen a response through the removal of an aversive stimulus. Therefore, the correct answer is A. Strengthen; strengthen. In the context of operant conditioning, reinforcement, whether positive or negative, is employed to increase the likelihood of a behavior occurring again in the future. An example of positive reinforcement could be giving a student praise for completing their homework, encouraging them to continue doing so in the future. Conversely, negative reinforcement involves the removal of an unpleasant stimulus, such as turning off an annoying alarm once a specific action is taken, thus encouraging the behavior that stops the unpleasant stimulus.