Final answer:
The sentence with a helping verb is 'We have voted for class president.'
Step-by-step explanation:
Out of the given sentences, the sentence that has a helping verb is: We have voted for class president.
In this sentence, the helping verb is 'have' which helps to establish the present perfect tense. The main verb is 'voted'.
Here is an example of a sentence without a helping verb: Alice understood the math problem. In this sentence, 'understood' is the main verb.
Learn more about Helping verbs