Which of these best describes the function of an auxiliary verb? It is a word used to label an action only. It is used to help form certain principle parts or tenses. It is also called a helping verb.

It is used to help form certain principle parts or tenses.

An auxiliary verb is either tense, aspect, modality, voice, emphasis, etc.

(:

"the sandy walls seemed to collapse in on themselves"

and

"the bloodshot waters seemed to have no bottom"