Indirect object is a noun or phrase referring to someone or something that is affected by the action of a transitive verb. In other words a noun or pronoun that follows an action verb.
I don’t want to be wrong but here’s my guess at some:
1) Paul gave CAROL a ticket to the concert.
2)Don’t tell ANYONE my secret.
3)He texted ME a picture of the TWO OF US at the concert
These are just some examples of indirect objects sorry if I’m wrong!
The sentence in which the underlined infinitive phrase functions as a subject is the last one - to quickly move large groups of people is the purpose of public transportation. <em>To quickly move </em>is the infinitive phrase, and it is a subject.