The correct answer is C. Winders.
Winders are triangular or trapezoidal steps that are used to change the direction of a staircase. They are typically used in spiral staircases, but they can also be found in L-shaped and U-shaped staircases. Winders can be either open or closed. Open winders have a gap between the tread and the riser, while closed winders have a solid tread and riser.
Round steps are circular steps that are typically used in spiral staircases. They are not used to change the direction of a staircase.
Angular steps are not a common type of step. They are similar to winders, but they have a more angular shape. They are not used to change the direction of a staircase.
Radial steps are a type of step that is used in spiral staircases. They are similar to round steps, but they have a more radial shape. They are not used to change the direction of a staircase.