Also, check if the user is in a country where certain open licenses apply, but that might complicate things. Better to keep it general.
I should also mention using YouTube for educational videos by teachers who might have covered the same topics. Maybe online communities or forums where educators share resources. For example, Reddit has communities where users share teaching materials. libro geografia e historia 2 eso santillana pdf tema 2 free
Next, what are the alternatives? Maybe suggest that they use official channels. Santillana might have some free samples or chapters on their website. Also, public libraries often have textbooks that can be borrowed. Some educational portals offer free access to parts of textbooks. I should list these options. Also, check if the user is in a