When Tim stepped onto the deserted campsite, the campfire was a mere glow of coals. The picnic table sat in disarray, covered by melted marshmallows and chocolate, empty drink cans, and half-eaten hot dogs. The sounds of water splashing and laughter echoed in the distance; Tim's friends had gone for a late-night swim. Tim could see flashlight beams bouncing on the water's surface. I guess I'll have to be the "grown-up," he muttered to himself. With an abrupt snap, Tim opened the garbage bag and began cleaning up after his friends. Which descriptive phrase from the scenario best represents lightheartedness?