S1 문장의 [______]에 들어갈 단어는?

난이도 고난도 · 힌트를 덜 열수록 높은 점수 (현재 5점)
The physical act of movement in the morning is not just beneficial for the body ─ it serves as a powerful stimulant for the brain, awakening it from the stillness of sleep and preparing it for the [______] of the day.