An infinitive is the base form of a verb plus

Noun

Adjective

Adverb

An infinitive or infinitive phrase is made up of the word "to" plus the simplest form of the verb that may act as an adjective, noun, or an adverb. It is based on a verb thus, expressing action/s or a state of being. Some examples of infinitives are to go, to like, to paint, to fly and a lot more. In the questions above, the sentence that has infinitive is in letter b. Tamar is planning to go to the zoo near her house.