You will be given a definition of a task first, then some input of the task.
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).

Context: Mukhavets ( Belarusian :  ( Muchaviec ) , ( muxavets ) ; Polish : Muchawiec , BGN / PCGN romanization : Mukhavyets ) is a river in western Belarus , a tributary to the Bug River . The river rises in Pruzhany , Belarus where the Mukha river and the Viets canal are converging , flows in the south - western Belarus and empties into the Bug River in Brest . The river is 113 km long . The basin area is 6,600 km² . The river is connected with the Dnieper river by the Dnieper - Bug Canal ., Poland, officially the Republic of Poland, is a country in Central Europe, situated between the Baltic Sea in the north and two mountain ranges (the Sudetes and Carpathian Mountains) in the south. Bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine and Belarus to the east; and the Baltic Sea, Kaliningrad Oblast (a Russian exclave) and Lithuania to the north. The total area of Poland is , making it the 69th largest country in the world and the 9th largest in Europe. With a population of over 38.5 million people, Poland is the 34th most populous country in the world, the 8th most populous country in Europe and the sixth most populous member of the European Union. Poland is a unitary state divided into 16 administrative subdivisions, and its capital and largest city is Warsaw. Other metropolises include Kraków, Wrocaw, Pozna, Gdask and Szczecin., The Bug River (or Western Bug "Zakhidnyy Buh, ") is a major European river which flows through three countries with a total length of ., Ukraine (tr. ) is a sovereign state in Eastern Europe, bordered by Russia to the east and northeast, Belarus to the northwest, Poland and Slovakia to the west, Hungary, Romania, and Moldova to the southwest, and the Black Sea and Sea of Azov to the south and southeast, respectively. Ukraine is currently in territorial dispute with Russia over the Crimean Peninsula which Russia annexed in 2014 but which Ukraine and most of the international community recognise as Ukrainian. Including Crimea, Ukraine has an area of , making it the largest country entirely within Europe and the 46th largest country in the world. It has a population of about 44.5 million, making it the 32nd most populous country in the world., Lithuania (UK and US: ), officially the Republic of Lithuania, is a country in Northern Europe. One of the three Baltic states, it is situated along the southeastern shore of the Baltic Sea, to the east of Sweden and Denmark. It is bordered by Latvia to the north, Belarus to the east and south, Poland to the south, and Kaliningrad Oblast (a Russian exclave) to the southwest. Lithuania has an estimated population of 2.9 million people , and its capital and largest city is Vilnius. Lithuanians are a Baltic people. The official language, Lithuanian, along with Latvian, is one of only two living languages in the Baltic branch of the Indo-European language family., Belarus ( lat. ', ), officially the Republic of Belarus, formerly known by its Russian name Byelorussia (though this name is no longer used in Belarus itself, even in Russian language), is a landlocked country in Eastern Europe bordered by Russia to the northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Its capital and most populous city is Minsk. Over 40% of its is forested. Its strongest economic sectors are service industries and manufacturing. Until the 20th century, different states at various times controlled the lands of modern-day Belarus, including the Principality of Polotsk (11th to 14th centuries), the Grand Duchy of Lithuania, the PolishLithuanian Commonwealth, and the Russian Empire., Subject: mukhavets river, Relation: mouth_of_the_watercourse, Options: (A) baltic sea (B) black sea (C) western bug
Output:
western bug