Which plan element does NIST single out as needing review more often than the plan as a whole?

Answer: C. Contact lists

SP 800-34r1 notes certain elements require more frequent review than others, singling out contact lists, and states plans for moderate- and high-impact systems should be reviewed more often.

Source: NIST SP 800-34 Rev. 1 (NIST) — Sec. 3.6 Plan Maintenance