Concept:Hair standing erect results from the contraction of arrector pili muscles, triggered mainly by a drop in body temperature.
Explanation:When a person enters an air-conditioned room, the surrounding temperature is low.
The skin detects this cold and stimulates the tiny arrector pili muscles attached to hair follicles.
These muscles contract, pulling the hair upright and causing "goosebumps."
In contrast, strolling in the sun, taking a hot drink, or doing strenuous exercise all raise body heat, which does not produce this response.
Answer:A. in an air-conditioned room