Answer:
A. Flashing beams bouncing
Step-by-step explanation:
This is the descriptive phrase that best represents light-heartedness. In this passage, we see that Tim is looking for his friends. Although he has a strict and responsible attitude, it is clear that his friends are instead relaxed and lighthearted. This idea is emphasized by the adjectives that are used to describe them. By saying that their flashing beams were "bouncing," the author conveys a positive and cheerful image that matches the mood of the friends.