yes it is
Bell tower.
solid
a building (that's funny)
iron
sheel
The Three Gorges Dams were made of concrete.
The structure of the tower is limestone or aliminium
The Eiffel Tower is a frame structure
If you are referring to the structure type of tower, they were/are often made of stone. If you are referring to the computer tower, they are either made of a metal such as aluminium or plastic.
The CN Tower in Toronto Canada is a concrete observation structure mainly used for TV and radio broadcasting. It also contains a number of cell sites.
Big Ben is a nickname for theGreat Bell in the tower clock at Westminster. The tower itself is often referred to as Big Ben
The cn tower is a shell structure, but it is also has materials piled up together so it is a shell structure and a mass structure.