Option 1: languorously -> means in a lazy, slow, relaxed manner without energy - opposite of vigorously.
Option 2: seriously -> means with earnest intent or solemnity - refers to attitude, not energy level.
Option 3: continuously -> means without stopping - refers to duration, not intensity.
Option 4: consistently -> means regularly or uniformly - refers to frequency, not energy level.
Hence, Option 1: languorously -> "Vigorously" means with great energy and force, while "languorously" means in a slow, relaxed, and lazy manner without energy - making them perfect antonyms -> correct