Here's why:
* Helping Verbs: Helping verbs (also called auxiliary verbs) work alongside main verbs to create verb phrases and provide more grammatical information. Common helping verbs include "be," "have," "do," and "will."
* Main Verb: The main verb expresses the action or state of being. In this sentence, the main verb is "worried," and it conveys the state of Sandra's emotion.
Since the sentence is in the simple past tense, "worried" acts as both the helping verb and the main verb.