Answer: A. are made of concrete and steel.
Explanation: Suspension bridges are typically constructed using materials such as concrete and steel. These materials provide the necessary strength and durability to support the bridge's structure and withstand various environmental conditions. The use of concrete and steel allows suspension bridges to span long distances and carry heavy loads, making them suitable for large-scale transportation projects.
Living bridges, on the other hand, are a unique type of bridge constructed using living vegetation, such as the roots of trees or plants. These bridges are formed by training and manipulating the growth of plants over time to create a natural bridge structure. Unlike suspension bridges, living bridges do not involve the use of concrete or steel as primary construction materials.