The correct answer is: D. On columns monolithically built with slab
A flat slab is a type of concrete slab that is supported directly by columns. The slab and columns are poured together as a single unit, which creates a monolithic structure. This type of construction is often used in commercial and industrial buildings, as it can provide a large, open floor plan with minimal columns.
The other options are incorrect because:
- A flat slab is not supported on beams.
- A flat slab is not supported on columns only.
- A flat slab is not supported on columns that are not monolithically built with the slab.