C. Greta and the campers she is with hide under the deck of the art house when they see a counselor's flashlight.
Explanation:
In the story "Fireflies", Greta and the rest of the campers were shown sneaking at night during their camping in Camp Kalawallah. While the short story provides a description of the camp and the inhabitants, one of the rules of the camp was not to be out at night.
The fact that Greta and the other campers were not supposed to be out at night is evidenced by the act of the campers sneaking out and hiding when they see the<em> "counselor's flashlight".</em> While trying to get to the <em>"fields and woods"</em>, the campers had to make sure that they were undetected by the counselors and safely evade any encounter with them.
