Christine, a seven-year-old girl, is upset because her parents are getting divorced. She has begun to wet the bed again, and she insists upon carrying her old security blanket. Christine is using the defense mechanism of

I believe the answer is: Regression

Regression refers to the process of slipping to our earlier stage of development when facing difficult situation rather than making an adaptation to face it.

This coping mechanism would make the person who do it act in non-suitable manner considering their age. Other example would be college students who throw temper tantrum like children when facing things that they considered as offensive.