Which of the following is NOT a characteristic of manhole covers?

The choice indicating that manhole covers are made from aluminum is correct because, while aluminum can be used for manhole covers, it is not the most common material. Most manhole covers are made from cast iron due to its durability and strength, which allows them to better withstand heavy loads and impacts. The circular shape of manhole covers is prevalent because this design prevents them from falling through the opening and allows for easier placement. Additionally, they are indeed designed to handle significant weight, such as the weight of vehicles passing over them, ensuring safety on roadways. Manhole covers also serve an essential function by sealing manholes, preventing unauthorized access and protecting the infrastructure below from elements and debris.