The pairs listed in the question are combinations of a river and the body of water into which it flows.

Option 1 suggests that both the Mekong River flows into the Andaman Sea and the Thames River flows into the Irish Sea. However, the Mekong River actually empties into the South China Sea, not the Andaman Sea. Similarly, the River Thames doesn`t flow into the Irish sea, it flows into the North Sea. As such, this option is incorrect.

Option 2 asserts that the Volga River flows into the Caspian Sea. This is accurate, the Volga is Europe`s longest river and it does indeed flow into the Caspian Sea. However, this option doesn`t account for other correct pairs.

Option 3 asserts that the Volga River flows into the Caspian Sea and the Zambezi flows into the Indian Ocean. This is correct, both of these river-sea pairs are accurately matched.

Option 4 includes the same incorrect pairing of the Mekong River and Andaman sea from option 1, while correctly stating that the Zambezi River flows into the Indian Ocean. As such, option 4 is only partially correct. So, option 3 is the most correct.