Option 1 -> indolent means lazy or avoiding work, which is the direct opposite of industrious.
Option 2 -> assiduous means hardworking and diligent, which is actually a synonym of industrious, not an antonym.
Option 3 -> positive means optimistic or affirmative, which is unrelated to the concept of being hardworking.
Option 4 -> domitable means able to be tamed or controlled, which has no connection to industriousness.
Hence, Option 1: indolent -> "Industrious" means hardworking and diligent, while "indolent" means lazy and avoiding work, making them perfect antonyms. The sentence suggests that without his hardworking nature, the project's outcome would have been different. -> correct