A dam is able to hold a large quantity of water because its wall is

The dam is able to hold a large quantity of water because its wall is thickest at the bottom. A dam is a large structure built across a river to store water. It is designed to hold back a large volume of water and withstand the pressure of the water it holds. The force exerted by the water on the dam increases with depth, so the wall of the dam needs to be thicker at the bottom to support the weight of the water. The wall of the dam is usually shaped like a triangle, with the base of the triangle at the bottom of the wall. This is known as a trapezoidal profile. The thickness of the wall gradually decreases towards the top of the dam. By making the wall thicker at the bottom, the dam can support the weight of the water and prevent it from flowing over the top of the dam. The thicker bottom part of the dam also provides a stable foundation for the structure, making it more resistant to damage from the pressure of the water. Therefore, the correct answer is "thickest at the bottom".