The author repeated the idiom about butterflies in Luisa's stomach three times throughout the story to show how Luisa's feelings of nervousness were decreasing as the day went on.

Idioms are groups of words that relate to a meaning which is not directly deducible. In other words, idioms express certain meanings that may or may not be literal but can be figurative.

In the short story "Second Day, First Impressions", the author talks about "butterflies" in Lisa's stomach three times.

Generally, "butterflies in the stomach" is an idiom that refers to a feeling of nervousness in the person.

This way, we can assume that Luisa is in fact nervous about the Scavenger hunt in her school.

But after reading through the story, we come to know that these butterflies in her stomach decreased as their scavenger hunt progresses.

Having butterflies in one's stomach means a person is nervous about a certain thing. And as such, the mentioning of butterflies in Luisa's stomach thrice throughout the story shows how her nervousness reduces as the day goes on. Thus, the correct answer is option C.

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