An infinitive can be used as all of the following except as a direct object. An infinitive can be used as nouns, adjectives, or adverbs. Option B is correct.
An infinitive will almost always begin with "to" followed by the simple form of the verb.
Whe it works as an adverb, it adds information about the verb. When it works as an adjective, it modifies a noun of a sentence.
Because an infinitive is not a verb, you cannot add s, es, ed, or ing to the end