Which of the following residential occupancies contains sleeping units that are for occupants who are primarily transient in nature?

The correct choice is Group R-1, as this classification specifically includes residential occupancies that are intended for transient occupants, meaning that the residents are typically staying for short periods of time. This may include hotels, motels, and other forms of lodging that cater to guests who are not permanent residents.

Group R-1 facilities often have common areas and are designed to provide services for these temporary occupants, which is a key aspect of their function. This differs from other residential groups like R-2, R-3, and R-4, which cater to longer-term or permanent residents and are typically structured for stability and community living rather than transient accommodation. This distinction is critical for understanding building code requirements and occupancy classifications.