Answer:
The infinitive phrase in the sentence above is "to go on a field trip" (B).
Explanation:
An infinitive phrase is a group of words that uses an infinitive. An infinitive phrase is a verbal that can act as a noun, an adjective, or an adverb. They can include objects or modifiers that make the phrase more descriptive. In this case, the infitive phrase functions as an adjective because it modifies the noun "plan".
