Choose the appropriate example of the Adverb of Reason-

He therefore left school.

The correct answer is Option (3) → He therefore left school.

Here's why:

• Adverb of Reason: These adverbs explain why something happened. They answer the question "for what reason?"
• The book is good enough: This doesn't explain the reason for anything, it simply describes the quality of the book.
• He was too careless: This describes the level of carelessness, not the reason behind an action.
• I was very exhausted in the evening: This describes the state of being, but doesn't explain a reason for anything.
• He therefore left school: "Therefore" clearly explains the reason why he left school, making it the Adverb of Reason in this case.