An infinitive phrase is a phrase in a sentence that uses an infinitive with modifiers or objects. An infinitive phrase can be used as a noun, adjective, or adverb.
For example:
Bach requested Tim to play the piano.
In the above sentence, the infinitive phrase is 'to play the piano' and it is used as a noun.
In the given sentence, <u>the infinitive phrase is 'to play quietly' and it is used as an adverb in the sentence. </u>
C because a market research helps when you are buying something which he is (car) and this is a secondary resource because it is recommended by someone rather than them finding the research himself.
