Question

Which sentence contains an infinitive or infinitive phrase?

A. Are you taking the cat to the vet?

B. The items to sell are on the table.

C. Special funding is available for that project.

D. The toolbox is waiting for you in the garage.

Answer 1

In English, infinitives always begin with the word "to" followed by a verb.
But the word "to" doesn't always signal an infinitive. For example, in answer A "to" is followed by an article and a noun. There is no verb after "to." In A "to the vet" is a prepositional phrase.

Answer C and D do not contain the word "to." Those answers cannot be true.

Now you just need to check B. Is the word after "to" a verb? If "sell" is a verb, you have found an infinitive.