The correct answer is A. the Rio Grande.
The Rio Grande is a river that flows from Colorado to the Gulf of Mexico. It forms the border between the United States and Mexico for more than 1,200 miles. The Rio Grande is the second longest river in Texas, after the Brazos River. It is also the longest river in the United States that is entirely within the country.
The Rio Grande is a major source of water for irrigation and drinking water. It is also a popular destination for fishing, boating, and swimming.
The Amazon is the largest river in the world by volume. It flows through Brazil, Peru, Colombia, Ecuador, Bolivia, and Venezuela. The Amazon is not a border river.
The Mississippi is the longest river in the United States. It flows from Minnesota to the Gulf of Mexico. The Mississippi is not a border river.
The Colorado is a river that flows from Colorado to the Gulf of California. It forms the border between the United States and Mexico for about 100 miles. The Colorado is not a major border river.