why did de Rubi choose to concentrate on protecting the land South of the Border line instead of trying to extend protection to the large amount of territory Spain controlled from Texas North to the Rocky Mountains

He didn't try to expand protection to the large amount of territory because Spain didn't have enough money or power to keep the northeastern presidios in Texas.

I don't actually know if this is right because my teacher doesn't actually check the questions, but this is what I understood from the lesson.

formulating the initial idea for the policy

answer is c.