b. It was the agreed border between French and Spanish territory in Texas.
Explanation:
Arroyo Hondo is widely known as a small stream located very close to or in between Natchitoches and Los Adaes in Louisiana. Around the eighteenth century(the 1700s) the main purpose of Arroyo Hondo is that it served as a boundary between French and Spanish territory in Texas.
Hence, the correct answer, in this case, is option B: It was the agreed border between French and Spanish territory in Texas.
