Final answer:
The infinitive can function as either a noun or an adjective in a sentence.
Step-by-step explanation:
The statement that the infinitive functions either as an adjective or as a noun is true. The infinitive is the base form of a verb preceded by the word 'to', and it can function as a noun or an adjective in a sentence. For example, in the sentence 'To win the race is my goal,' the infinitive 'to win' is functioning as a noun, while in the sentence 'She has books to read,' the infinitive 'to read' is functioning as an adjective modifying the noun 'books'.