Five-year-old jared begins to suck his thumb when his parents bring his newborn sister home from the hospital. jared is relying on the defense mechanism called

The defense mechanism is called REGRESSION.

In psychology, regression is the return to modes of thought and conduct that do not correspond to the age or psychic maturity of the individual, it means the behavior that is usual in a given situation gives way to behavior that is characteristic of a previous stage of development or corresponds to a repertoire of activities acquired in the past of the individual (like thumb sucking for Jared, he use to do that when he was a baby), but gradually replaced by more adapted activities. It may be temporary or lasting.

Ithink the answer is nuclear membrane