Affective domain focuses on adoption of a value system as a part of life style…

Concept: Krathwohl's Taxonomy of the Affective Domain arranges instructional objectives into five hierarchical levels, ordered by increasing internalization of a value or attitude: Receiving, Responding, Valuing, Organization, and Characterization (by a value or value complex). Each higher level marks a deeper, more consistent internalization of the value, moving from simply being aware of it toward the value becoming a stable, defining part of the learner's personality and everyday conduct.

Applying it here: the question asks which level corresponds to a value system being adopted "as a part of life style" — that is, the value has been internalized so completely that it consistently governs the person's behaviour across situations and becomes integrated into their overall character and way of living. That complete, lasting integration into one's total conduct and philosophy of life is exactly what Characterization (by a value or value complex) describes: at this level the internalized value system controls behaviour predictably over time until it becomes characteristic of the person's lifestyle.

Cross-check — why the other levels stop short of a full lifestyle change:

• Describing willing, active participation in a value-related activity (for example, readily following a rule) without the value yet being judged worthy or built into a lasting way of living captures only voluntary engagement, not a value system shaping one's whole lifestyle.

• Describing the act of attaching worth or importance to one particular object, idea, or behaviour — coming to prize or commit to it — stops at a single valued item; it does not yet organize that value together with others into a complete system that consistently directs conduct.

• Describing the bringing together of several values, comparing them, resolving conflicts among them, and building them into an internally consistent system is an important integration step — but the system formed at this stage has not yet stabilized into a lasting, characteristic way of living.

Result: only Characterization matches a value system being adopted "as a part of life style," so that is the correct level.