The Amazon River has several important tributaries that contribute to its vast water flow. Among the given options:
- Purus River is a major tributary of the Amazon and flows through Peru and Brazil.
- Paru River is also a tributary of the Amazon but is less significant compared to Purus.
- Juruika River does not exist as a well-known Amazon tributary.
- Paraná River is incorrect as it is one of the major rivers in South America but flows separately, mainly through Brazil, Paraguay, and Argentina, and is not a tributary of the Amazon.
Thus, the correct answer is Purus River.