[38∼39] 글의 흐름으로 보아, 주어진 문장이 들어가기에 가장 적절한 곳을 고르시오. 38. It is the reason that individuals with certain forms of blindness do not entirely lose their circadian rhythm. Daylight isn’t the only signal that the brain can use for the purpose of biological clock resetting, though it is the principal and preferential signal, when present. (①) So long as they are reliably repeating, the brain can also use..