Four-year-old Timmy had not wet his bed for over a year. However,he started bed-wetting again soon after his sister was born. Timmy's behavior best illustrates

A) reaction formation.
B) projection.
C) regression.
D) denial.

Regression involves a return to an earlier stage of development in response to stress or a crisis. Timmy's bed-wetting behavior, which he had not exhibited in over a year, returned after the birth of his sister. This suggests that he may be regressing to an earlier stage of development as a way of dealing with the stress and changes brought about by the new family dynamic.