7. Which sentence contains an infinitive phrase? He went to Congress so that he could gather support for his proposal. He went to Congress and gathered support for his proposal. He visited Congress to gather support for his proposal

The following sentence contains an infinitive phrase:

C. He visited Congress to gather support for his proposal.

An infinitive phrase is a group of words that uses an infinitive ("to" + verb). An infinitive is a verbal (a word that expresses action); so, an infinitive phrase has the same role of expressing action in a sentence. An infinitive phrase is just a part of a sentence, working like a noun, adjective, or adverb.

In this case, is "to + gather".