题目:Among the following rivers, _____ forms a natural boundary between Mexico and the U.S.
[A.the Potomac, B.the Columbia, C.the Rio Grande River, D.the Colorado]$[C]
题目:Among the following rivers, _____ forms a natural boundary between Mexico and the U.S.
[A.the Potomac, B.the Columbia, C.the Rio Grande River, D.the Colorado]$[C]