What system type allows two or more systems to be combined in one building?

The correct answer focuses on the ability of combined automatic sprinkler systems to integrate multiple systems into a single framework within a building. This system type allows for the interaction of various sprinkler types or configurations working cohesively to provide enhanced fire protection throughout the structure.

Combined automatic sprinkler systems are particularly advantageous because they can incorporate different types of sprinklers, such as wet and dry systems, within the same building design, effectively addressing diverse fire risks and environmental conditions. This flexibility is crucial in modern building designs where a single fire protection strategy may not suffice due to varying occupancy risks across different areas of the building.

Other types listed, such as the single-system approach, modular systems, and integrated systems, do not specifically denote the capability to combine multiple systems distinctively within one building for enhanced fire safety. Therefore, combined automatic sprinkler systems are recognized for their functionality and adaptability in providing comprehensive fire protection solutions.