Which two of these sentences contain an infinitive?

1. amy put in a lot of hard work to earn her bachelor’s degree in computer science.
2. classic rock songs soothed emmett’s stormy moods on dark, gloomy afternoons.
3. joel was in shock when his parents announced the upcoming move on christmas eve.
4. it was claudia’s childhood dream to write her favorite author’s biography someday.

The sentences that contain an infinitive are:

1. Amy put in a lot of hard work to earn her bachelor’s degree in computer science.

4. It was Claudia’s childhood dream to write her favorite author’s biography someday.

Explanation:

The infinitive is the base form of a verb, that can be used alone (the zero infinitive) or with to (the to-infinitive.) Infinitives can be used as adjectives, adverbs or nouns with the intent to indicate the intention of the action - like sentence 1-, as the subject of the sentence, to indicate what something will be used for, among other uses.