The best way to increase response strength in self-modification is through 

A) positive reinforcement.
B) finding a reward effective for that person.
C) choosing a readily available reinforcer.
D) all of these.

The best way to increase response strength in self-modification is through a combination of positive reinforcement, finding a reward effective for that person, and choosing a readily available reinforcer. Using positive reinforcement involves rewarding one's own behavior after completing a task or achieving a goal, which increases the likelihood of that behavior being repeated in the future. However, the reward chosen must be effective for that person, something that is meaningful to them, and readily available to maintain the behavior change. Using all three strategies together is the most effective way to increase response strength in self-modification.