Which of the following counties of south west England are mostly bordered by the Tamar River?

The south-west of England is one of nine official regions of England, where the regions were formerly known as the government offices regions. Between 1994 and 2011, nine regions had officially devolved functions within government. The south-west England is the largest covering 9,200 square miles (23,800 km2). It consists of the counties: Bristol, Cornwall, Dorset, Devon, Gloucestershire, Sommerset and Wiltshire; as well as the Isles of Scilly.

The Tamar is a river in the south-west of England, that forms most of the border between Devon (to the east) and Cornwall (to the west).The total length of the river is 61 miles (98 kms). At the mouth, the Tamar flows into Hamoaze before entering Plymouth Sound, a bay of the English Cannel. The name Tamar was mentioned by Claudius Ptolemy in the second century in his geography, who was a mathematician, astronomer, geographer, and astrologer. The Devon is reaching from the Bristol Channel in the north to the English Channel in the south and bounded Cornwall to the west. The Cornwall is bordered to south by the English Channel and to the east by the Devon. The bordered area of the Devon and the Cornwall is World Heritage Site due to its historic mining activities.