Over the course of time, this process would have helped to [______] water on Earth, while it also contributed to the emergence of oxygen in the atmosphere.
동의어 · keep, hold, preserve파생어 · retention(보유, 유지)
★ 주제문 — S2·S3·S4·S5·S6이(가) 이 문장을 떠받칩니다 — S1을(를) 맥락(으)로 뒷받침