Choose the appropriate example of the Adverb of Reason-

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

An adverb is a word that tells how, when, where or how much something happens. It can also describe an adjective or another adverb, for example she sings sweetly, very hot.

Adverb of reason:

• An adverb of reason tells us why something happens.
• Common adverbs of reason: therefore, hence, consequently.
• This sentence: "therefore" shows that he left school because of something said before.

Why the Other Options are Incorrect?

Option 1: The book is good enough. — Incorrect. "Enough" is an adverb of degree: it tells how good the book is.

Option 2: He was too careless. — Incorrect. "Too" is an adverb of degree: it tells how careless he was.

Option 4: I was very exhausted in the evening. — Incorrect. "Very" is an adverb of degree, and "in the evening" tells the time. Neither gives a reason.