Answer: I would contend that the right answer is actually the B) Threatening mood.
Explanation: Just to elaborate a little on the answer, it can be added that the imagery suggests the imminent outbreak of an inclemency, such as a storm, which certainly may represent a threat. The few people that were out walking hurried "dismally and silently," which also indicates the seriousness of the scene. By describing the weather in such sensorial way—one can almost feel the wind and hear the hasty steps of the pedestrians—the author successfully created a threatening mood.
