Body's thermoregulation in hot conditions

Steps:

• Identify responses for cooling in heat: vasodilation increases skin blood flow for heat loss; sweating enables evaporative cooling; hair erector relaxation reduces insulation.
• Note description 1 (arteries dilate) and 5 (sweat evaporates) match heat response; 4 (hair relax) also fits but not in all options.
• Description 2 is undefined in the query, making choices C and D ambiguous.
• Eliminate A (1,3,6: mixes heat with cold responses like hair contraction and shivering).

Not enough information to confirm D, as 2 is missing.

Final answer: Not enough information.