* Helping verbs assist the main verb in a sentence. They provide information about tense, mood, or voice.
Let's look at why the other options are incorrect:
* a. Give: This is a main verb. It can stand alone in a sentence (e.g., "They give gifts.").
* b. Appear: This is also a main verb. (e.g., "They appear happy.")
* d. Have: While "have" can be a helping verb in some cases (e.g., "They have finished"), it can also be a main verb (e.g., "They have a lot of work.").
Examples of "do" as a helping verb:
* Do you like pizza? (Do helps form the question)
* They do not understand. (Do helps form the negative)
* We do want to go. (Do emphasizes the action)