The Aras River forms part of the border between which countries?

The Okavango River flows through which countries? The Indus River flows through which countries? The Niger River flows through which countries? The Amur River forms part of the border between which countries? The Limpopo River forms part of the border between which countries? The Sava River forms part of the border between which countries? The Ubangi River forms part of the border between which countries? Which river flows through Peru, Brazil, and Colombia before emptying into the Amazon River?