How does ambient temperature affect conductor ampacity, and what NEC practice addresses this?

How does ambient temperature affect conductor ampacity, and what NEC practice addresses this?

• A. Higher ambient temperature increases ampacity; use temperature derating tables to adjust downward.
• B. Ambient temperature has no effect on ampacity.
• C. Higher ambient temperature reduces ampacity; use temperature derating tables to adjust ampacity.
• D. Ampacity is only affected by insulation thickness.

Answer: (C)