万(まん)一(ひと) manhito雨(あめ) ameが ga降(ふ)れ()ば() fureba、園(えん)遊(ゆう)会(かい) enyuukaiは wa行(おこな)わ()れ()な()い() okonawarenaiでしょう deshou。 If it happens to rain, the garden party probably won't be held. weathersocial eventshypothetical situations~ば (conditional)万一 (if by chance)園遊会 (garden party)