The sentence in which the underlined infinitive phrase functions as a subject is the last one - to quickly move large groups of people is the purpose of public transportation.
<em>To quickly move </em>is the infinitive phrase, and it is a subject.
D. ALL OF THE ABOVE.
A verbal phrase consists of a verbal and a modifier or any object. Verbal is the term used to define a verb form that does not function as a verb in a sentence. Instead it functions as a noun, adjective, or adverb.
Three types of verbal phrase
Gerund phrase - consists of a gerund (-ing) and a modifier or object. Functions as a noun and can be a subject, subject complement, object, or appositive int he sentence.
Infinitive phrase - begins with an infinitive and is followed by an object or modifier. It almost always begin with "to" and is followed by the verb.
Participial phrase - always functions as an adjective in the sentence; consists of past or present participle with any object or modifier.
