Which one is an auxiliary?

Explanation

The correct answer is 'Do.' In this question, 'Do' is the only auxiliary verb among the options provided. Auxiliary verbs, also known as helping verbs, are used alongside main verbs to create questions, negative statements, and various verb tenses. The other options, 'With,' 'On,' and 'For,' are prepositions that show the relationship between nouns or pronouns and other elements in a sentence.