My sister Natalyn is training to run a marathon, so she hired a personal coach and a nutritionist.

Choose the infinitive phrase in the sentence.

A) she hired

B) is training

C) to run a marathon

D) coach and nutritionist

The correct answer is "To run a marathon"

Explanation:

An infinitive phrase is formed by the preposition "to" + the bare verb+object.

Infinitive phrases can act as nouns, adjectives and adverbs.

In this example, the infinitive phrase is functioning as an adverb since it is explaining "why" Natalyn is training.

The rest of the options are not infinitive phrases.

Option A is formed by subject+verb in past tense

Option B is formed by present continous

And option D is formed by the nouns "coach" and "nutricionist"

C) To run a marathon is the right answer