We all made an effort "to work harder"

Identify the phrase in quotations

A. prepositional phrase

B. verb phrase

C. infinitive phrase

D. gerund phrase

Prepositional phrases begin with a preposition (above, behind, below)

a verb phrase contains a verb and an object, but no subject

an infinitive phrase starts with "to" and has a verb

a gerund phrase contains a verb ending in "-ing"

with that information, only one answer fits "to work harder" and the answer is C! it begins with "to" and contains a verb.