Query: Along with Plymouth and Devonport, what location was merged into a county borough in 1914?
Context: Throughout the Industrial Revolution, Plymouth grew as a commercial shipping port, handling imports and passengers from the Americas, and exporting local minerals (tin, copper, lime, china clay and arsenic) while the neighbouring town of Devonport became a strategic Royal Naval shipbuilding and dockyard town. In 1914 three neighbouring independent towns, viz., the county borough of Plymouth, the county borough of Devonport, and the urban district of East Stonehouse were merged to form a single County Borough. The combined town took the name of Plymouth which, in 1928, achieved city status.