The Niger River flows through which countries?

The Paraná River forms part of the border between which countries? The Tigris River flows through which countries? The Okavango River flows through which countries? The Indus River flows through which countries? The Amur River forms part of the border between which countries? The Aras 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?