An infinitive phrase has much the same form as a prepositional phrase beginning with the preposition to and serves much the same function.

An infinitive phrase has much the same form as a prepositional phrase beginning with the preposition to and serves much the same function is false. A prepositional phrase will begin with a preposition and ends with a noun, pronoun, gerund or clause whereas the infinitive phrase begins with the infinitive (to).

i'm pretty sure it is 1) wants to hide her true feelings about robert. i'm sorry if it is wrong. good luck! : d