Identify the infinitive phrase in the sentence below. We need to monitor fishing and mining carefully.

a. we need

c. carefully

b. to monitor fishing and mining carefully

d. none of these

The infinitive phrase in the sentence is (b) to monitor fishing and mining carefully. An infinitive phrase always starts with the word "to" and then followed by any modifiers and complements. It could also be used as a noun, an adjective or an adverb.