In this task, you are given a context, a subject, a relation, and many options. Based on the context, from the options select the object entity that has the given relation with the subject. Answer with text (not indexes).
Q: Context: Europe is a continent that comprises the westernmost part of Eurasia. Europe is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, and the Mediterranean Sea to the south. To the east and southeast, Europe is generally considered as separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways of the Turkish Straits. Yet the non-oceanic borders of Europea concept dating back to classical antiquityare arbitrary. The primarily physiographic term "continent" as applied to Europe also incorporates cultural and political elements whose discontinuities are not always reflected by the continent's current overland boundaries., Lake Kastraki ( Greek :   ) is an artificial lake near Kastraki in Aetolia - Acarnania , western Greece . The lake is drained by the river Acheloos , and fed by the rivers Acheloos and Inachos . It was formed by the Kastraki Dam , completed in 1969 . Its area is about 28 km² and its maximum capacity is 950,000,000 m³ of water . It is used for the generation of hydroelectric power by DEI ., Aetolia-Acarnania is one of the regional units of Greece. It is part of the geographic region of Central Greece and the administrative region of West Greece. A combination of the historical regions of Aetolia and Acarnania, it is the country's largest regional unit. Its capital is Missolonghi for historical reasons, with its biggest city and economic centre at Agrinio. The area is now connected with the Peloponnese peninsula via the Rio-Antirio Bridge. The surrounding regional units take in Arta in Epirus, a narrow length bordering Karditsa of Thessaly, Evrytania to the northeast, and Phocis to the east., Acarnania is a region of west-central Greece that lies along the Ionian Sea, west of Aetolia, with the Achelous River for a boundary, and north of the gulf of Calydon, which is the entrance to the Gulf of Corinth. Today it forms the western part of the regional unit of Aetolia-Acarnania. The capital and principal city in ancient times was Stratos. The north side of Acarnania of the Corinthian Gulf was considered part of the region of Epirus., Greece (' ), officially the Hellenic Republic (Greek: ' ), historically also known as Hellas ("" ), is a country in southeastern Europe. 
Greece's population is approximately 10.955 million as of 2015. Athens is the nation's capital and largest city, followed by Thessaloniki., Subject: kastraki , Relation: lake_inflows, Options: (A) achelous river (B) ural river
A:
achelous river