Correct Option: C

A flat arch has usually the angle formed by skewbacks as 60° with horizontal, thus forming an equilateral triangle with intrados as the base. The intrados is apparently flat, but it is given a slight rise of camber of about 10 to 15 mm per metre width of Opening to allow for small settlements. However, the extrados is kept horizontal and flat. Flat arches are used only for light loads, and for spans upto 1.5 m.