Internalization can be defined as:

Internalization refers to the process in which individuals incorporate external beliefs or values into their own personal belief system, effectively making those beliefs a part of their identity and guiding their behavior. When a belief is internalized, it becomes an integral component of a person's values, influencing their decisions and actions in a consistent manner.

The first choice, which states that internalization is integrating a belief into personal values, directly captures this essence. It emphasizes the transformation of external ideas into personal convictions. This process often occurs through socialization, where individuals learn and take on values from their families, communities, or cultures, leading to behaviors that reflect these internalized beliefs.

In contrast, the other options describe different psychological processes. Accepting beliefs without question pertains more to uncritical acceptances, such as conformity, but does not imply the deeper integration of these beliefs into one's identity. The adoption of behaviors temporarily for acceptance reflects a situational conformity rather than internalization, as it might not involve a change in personal belief systems. Finally, mimicking others' behaviors without understanding describes a superficial imitation, lacking the depth of personal integration associated with internalization.