The helping verbs in this sentence are the verbs "had" and "were".
Verb phrases include two or more words that refer to an action. In these phrases, the helpng verb or auxiliary verb is the word that extend the meaning of the main verb.
In this sentence there are two main verb phrases "had heard" and "were arriving", and in these the main verbs are "heard" and "arriving" because they directly describe the action. Therefore "had" and "were" are just helping verbs.
Learn more about helping verbs in: https://brainly.com/question/14061315
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