C. Ledged and braced
This question was posed to me in an internship interview.
This interesting question is from Parts of Window topic in section Doors, Windows and Ventilators of Construction & Building Materials
Explanation: The braces are generally 100 mm to 150 mm wide and 30 mm thick. The braces give rigidity to the door and hence the doors of these types are useful for wide openings. The braces are usually housed in the ledges.