Maybe this can be chalked up to being an older test with looser standards of precision than today, but I really think this is a deeply flawed question:
The word "skeptical" in (E) is far too weak to approach correctness; note the line that states "Obviously, a more complex societal shift is taking place than the theory of Pan-Indianism can account for." How can the weak "skeptical" in (E) be reconciled with the forceful "obviously" in the passage?
Meanwhile, you can find solid support that the author is uncomfortable with the aspect of Pan-Indianism that suggests that the increase in cultural borrowing across tribes will lead to the inevitable outcome of "the eventual dissolution of tribes and the complete assimilation of native Americans into Euroamerican society." See the last sentence of P3, for example.
If I'm way off base here, please tell me where I'm going wrong. But I've read this passage over and over and can't square how (E) more accurately describes the author's attitude toward the theory of Pan-Indianism than (B). Thanks in advance!