Why was the cleaner sweeping the station at that time?

The correct choice highlights that the presence of the cleaner sweeping the station was in accordance with their established work schedule. Train stations operate under meticulous maintenance routines; custodial staff have designated times for cleaning duties to ensure that the station remains safe, presentable, and functional for travelers. This consistent schedule helps prevent issues, such as dirt accumulation or safety hazards from spills, thereby contributing to a pleasant environment for passengers.

In the context of the other options, while a busy time or an upcoming event might necessitate additional cleaning, these are not definitive reasons for the cleaner's activities at that specific moment. Similarly, preparing for inspections, although important, does not specifically account for the regularity of a cleaner’s duties as per their work schedule, which ensures cleaning happens consistently rather than only in response to particular events or inspections.