Question

When the suffix -ly is added to an adjective such as clever, the word

Answer 1

It becomes an adverb, because if you think about it, you're adding something to the meaning of the word!
Definition of:
Adverb: A word or phrase modifying an adjective, verb, adverb, or word group!

Answer 2

When the suffix -ly is added to an adjective such as clever, the word becomes and adverb. Option A is correct.

An adverb is the part of a speech that modifies, describes or provides more information about adjectives, verbs, and other adverbs. Usually, adverbs ending in the suffix LY refers to how something is done. For instance, cleverly, properly, angrily, anxiously. badly, beautifully and the like.