Behavior therapists seek to reinforce desirable behavior in order to __________

A) increase its magnitude.
B) increase its duration.
C) increase its frequency.
D) control it.

Behavior therapists seek to increase the frequency of desirable behavior, as this means that the behavior is occurring more often and becoming a more consistent part of the individual's repertoire. Increasing the magnitude or duration of the behavior may be desirable, but the primary goal is to increase its frequency. While behavior therapists do seek to control behavior, this is not the best answer as it is too general and does not reflect the specific goal of reinforcing desirable behavior.