Answer :
Answer:
C). Infinitive phrase.
Explanation:
An infinitive phrase is defined as the phrase that comprises of an infinitive(the basic form of the verb) along with its object and the modifier. Such phrases function as a noun, adverb, or as an adjective in the sentence.
In the given sentence, the category of verbal phrase that has been underlined 'to show us the lava flow' would be 'infinitive phrase' that functions as an adverb in the sentence. It justifies the above definition appropriately as it involves an infinitive 'to show' accompanied by the direct object 'us' followed by the indirect object 'the lava flow'. Thus, option C is the correct answer.