Possible Clues:

• Neighbor of Arg.
• Arg. neighbor
• Braz. neighbor
• Neighbor of Arg. and Braz
• Neighbor of Braz. and Arg
• Second-smallest S.A. country
• Montevideo's land: abbr.
• Country south of Braz
• Neighbor of Braz.
• Country on the Rio de la Plata: Abbr.