For a stack of books, you would use "estos" if the books are near you (masculine plural), or "esos" if they're further away (masculine plural).
If you want to specify "those ones over there," you would use "aquellos."
So the correct choice would be:
- estos (if the stack of books is near)
- esos (if the stack of books is farther away)
- aquellos (if the stack of books is far away)
If you are referring to a feminine noun, you would use:
- estas (if it’s near)
- esas (if it’s farther away)
- aquellas (if it’s far away)
Since "stack of books" is masculine plural, "estos," "esos," and "aquellos" are the appropriate options.