What does the symbol '//////' represent?

The symbol '//////' is commonly used in blueprints and technical drawings to represent firebrick. Firebrick is a type of brick that can withstand high temperatures and is often used in the construction of fireplaces, kilns, and other high-heat applications. This graphical representation helps convey specific instructions about materials and construction techniques, thereby aiding builders and contractors in understanding the specifications of the project.

The other symbols in the choices correspond to different components in building plans. For example, a water tank would have its own unique symbol distinct from firebrick, as would electrical conduits and air ducts. Knowing the correct representation is essential for interpreting blueprints accurately and ensuring that the right materials are used in construction.