Answer:
Happily
Explanation:
It describes how something is happening. He is not just thinking, he is happily thinking.
<span>Since adjectives tell us how much or how many of something you're talking about, "many" which comes before the noun "books" is the adjective. On the other hand, adverbs answer the question: How, When, Where, To what extent, or magnitude, so the word "there" answers the "where" question. It modifies the adjectives and verb.</span>
