The correct answer is A. Straight stairs are the most comfortable type of stairs because they are the easiest to walk up and down. They are also the most common type of stairs, and they are relatively easy to build.
B. Dog-legged stairs are a type of stair that has two or more flights that are connected by a landing. They are not as comfortable to walk up and down as straight stairs, but they can be used to save space in a small area.
C. Geometrical stairs are a type of stair that has a unique shape, such as a spiral or a helix. They are not as comfortable to walk up and down as straight stairs, but they can be very stylish.
D. Open newel stairs are a type of stair that does not have a solid newel post at the bottom of the stairs. They are not as comfortable to walk up and down as stairs with a solid newel post, but they can be more open and airy.