Correct option is D
12 DT 20 indicates frame of double shutter door with a width of 12 modules and height of 20 modules.
As per IS standard specifications for timber door, window and ventilator frames, the symbolic designation of 12 DT 20 would indicate:
12 DT 20 indicates frame of double shutter door with a width of 12 modules and height of 20 modules.
The minimum density (g/cc) of corrugated and semi-corrugated asbestos cement sheets considered acceptable for construction purposes by the Indian standard is: