Which defense mechanism involves reversion to an earlier phase of psychological development?

A) repression
B) regression
C) displacement
D) projection

Regression is the defense mechanism that involves reversion to an earlier phase of psychological development. This can manifest in behaviors such as temper tantrums, clinging to caregivers, or using language from an earlier developmental stage. Repression involves pushing unacceptable thoughts or feelings into the unconscious mind, displacement involves redirecting emotions from a threatening object to a less threatening object, and projection involves attributing one's own undesirable thoughts or feelings onto someone else.