choices.label: A B C D
choices.text: nile:africa mississippi river:united states volga:russia panama canal:panama
explanation: the "yangtze river" is the longest natural river in "china", and the entire basin of the "yangtze river" is located in "china". "nile" is the longest river in "africa", but "africa" ​​is not a country, "nile" and "africa" ​​have no logical relationship. the "mississippi river" water system not only flows through 31 of the 48 states in the continental “united states”, but also through two states in canada. the "volga" is the longest natural river in "russia", and its basins are all located in "russia". the "volga" and "russia" are related in some way, and "russia" is a country. the "panama canal" is man-made, not a natural river.
relation: yangtze river china R3.10
relation: volga russia R3.10