Rio Grande River - forms most of Texas’s ______________ boundary
fill in the blank
southern
Sabine River - helps form the boundary between Louisiana & _________
fill in the blank
Texas
Rio Grande River - forms most of Texas’s southern boundary
To answer this question, you can do a quick online search using a search engine such as Google. Type in "Rio Grande River" and look for reliable sources like government websites or reputable educational resources. Once you find a reliable source, you can search within the text to find the specific information you are looking for.
In this case, the Rio Grande River forms most of Texas's southern boundary.