Which of the following sentences contains an infinitive?

A. Heather wants to go to the store with us.

B. The car was parked next to the church.

C. Dave will take us to the field before the game.

D. Let's walk to the picnic.

An infinitive is always going to begin with the word " to " followed by the simple form of a verb. It can act as a noun, adj, or adv.

So ur infinitive would be : A. Heather wants to go to the store with us.

ur infinitive is " to go " and it is functioning as a noun (the direct object).