Answer: The right answer is the D. It introduces the conflict.
Explanation: Just to elaborate a little on the answer, it can be added that this excerpt is important because it is possible to infer that a troubling and significant scene, possibly an accident, has just happened. The trash collector had just being absorbed in his thoughts, and he was about to resume his duties when a flash, possibly from a vehicle, fell on him, and took from him "what the morning had offered"—the chance to have some time, perhaps just a few minutes, to be immersed in his thoughts.
