Answer:

Introduction:
In this question, we are given four options, and we have to identify which one is not a type of stairs. Let's analyze each option to determine the correct answer.

Options:

a) A full turn: A full turn refers to a staircase that makes a complete 360-degree turn. It is also known as a spiral or helical staircase. This type of staircase is commonly used in tight spaces where a straight staircase is not feasible. A full turn is a valid type of stairs.

b) Open newel: An open newel is a design element that is used in staircases. It refers to the space left between the steps and the newel post, which is the central supporting pillar of the staircase. It provides an open and airy look to the staircase. Open newel is a valid type of stairs.

c) Dog-legged: A dog-legged staircase is a type of staircase that changes direction by 180 degrees. It consists of two flights of steps that are connected by a landing in the middle. This design allows the stairs to change direction without the need for a full turn. Dog-legged is a valid type of stairs.

d) Three-quarter landing: A three-quarter landing staircase is a design that includes a landing between two flights of steps, forming a 90-degree turn. This type of staircase is used when there is not enough space for a full turn or dog-legged staircase. Three-quarter landing is a valid type of stairs.

Conclusion:
After analyzing all the options, we can conclude that option 'A': A full turn is not a type of stairs. The other three options, open newel, dog-legged, and three-quarter landing, are all valid types of stairs commonly used in different architectural designs.