Which of the following sentences contains an infinitive?
a. heather wants to go to the store with us.
b. dave will take us to the field before the game.
c. let's walk to the picnic.
d. the car was parked next to the church.

The sentence that contains an infinitive is letter A: Heather wants to go to the store with us. Infinitive phrases starts with infinitives that is, “to” added by a simple verb and can be used as nouns, adjectives or adverbs. In the case of including a main clause in the sentence, infinitive phrase separates it with comma. It is not participial because it (phrase) did not start with a participle and not a gerund because the first word of the phrase has no ‘-ing’.