sentences:  A block is a symmetrical building, consisting of two quadrangles surrounded by corridors, similar to cloisters, which originally had no windows and were open roofed; both have since been installed.The main hall is the home of the largest stage in the school, with an additional gallery at the back.In the late 1970s, a large extension was added to the eastern side of ‘A Block’; this extension is known as ‘C block’.