17. In which sentence is the entire infinitive phrase underlined?

The best preparation for a game is to practice until you know all the plays.

The crowd was excited to see a great play.

To cheer good plays made by both teams is good sportsmanship.

The best preparation for a game is to practice until you know all the plays.

The crowd was excited to see a great play.

To cheer good plays made by both teams is good sportsmanship.

Explanation:

An infinitive phrase is a set of words, with an infinitive as its main part and with some modifiers and complements as an addition. All these words act as one phrase and have one function in a sentence (infinitive phrase can act as a noun or an adjective or an adverb).

Since nothing is underlined in these answers, let's find infinitive phrases for each of them:

-The best preparation for a game is to practice until you know all the plays - infinitive here is "to practice" but if we want to be more precise on the amount of practice and to modify this infinitive, then our phrase would be "to practice until you know all the plays".

- The crowd was excited to see a great play - the infinitive is "to see" but we don't know what, so the entire phrase is "to see a great play"

- To cheer good plays made by both teams is good sportsmanship - the infinitive is "to cheer" and the sentence "To cheer is good sportsmanship" could be valid. But, if we want to be more precise, we would say "to cheer good plays". Of course, we can go into even more details and say the entire phrase "to cheer food plays made by both teams"