Context: Plymouth lies between the River Plym to the east and the River Tamar to the west; both rivers flow into the natural harbour of Plymouth Sound. Since 1967, the unitary authority of Plymouth has included the, once independent, towns of Plympton and Plymstock which lie along the east of the River Plym. The River Tamar forms the county boundary between Devon and Cornwall and its estuary forms the Hamoaze on which is sited Devonport Dockyard.

Question: What river is to the west of Plymouth?
Answer: River Tamar

Question: To the east of Plymouth lies which river?
Answer: River Plym

Question: The River Tamar is the boundary between Devon and what other county?
Answer: Cornwall

Question: In what body of water do the rivers Plym and Tamar meet?
Answer: Plymouth Sound

Question: When did Plymstock join the unitary authority of Plymouth?
Answer: 1967