Final answer:
The main intervention described in the question is to increase the intensity, frequency, and alter the target of a behavior or action. This approach is most effective in individuals open to suggestion.
Step-by-step explanation:
The main intervention described in the question is C. increase the intensity, increase the frequency, alter the target. This intervention involves gently nudging an individual to do more of what is working, by increasing the intensity and frequency of the particular behavior or action, and also altering the target or focus. This approach is most effective in individuals that are very open to the power of suggestion.