I have told you now and again that you must not read such trash. (Identify the word class of the underlined words 'now and again')

The phrase 'now and again' means 'occasionally' or 'from time to time' and modifies the verb 'have told', indicating the frequency of the action. Words or phrases that modify verbs by answering questions like 'when', 'how often', or 'how' are adverbs (or adverbial phrases). Therefore, 'now and again' functions as an adverb in this sentence.