Which of the following shapes is used in towers, bridges and buildings?

If we observe our surroundings, we will see that a triangular shape is used in the making of bridges, towers, and buildings. Because they maintain their shape and angle when pressure or force is applied to any one of their vertices, triangular shapes are an ideal choice for bridges, towers, and buildings. Other shapes, such as squares, pentagons, hexagons, etc., aren't as well suited for building since pressure given to any one of their vertices causes them to eventually change shape.
Hence, the correct answer is option A.