This passage is confusing because there are many different things. Tribe chiefs, chief's council, and shaman; political affairs and religion affairs, presettlement and aftersettlement, etc. You need to be careful which is which when you answer questions.
26. The author of the passage implies that which of the following occurred after the Iroquois were resettled on reservations early in the nineteenth century?
(A) Chiefs became more involved in their tribes’ religious affairs.
Wrong. "In the longhouse, the tribe’s chief influenced both political and religious affairs." That was before the settlement.
(B) The authority of the chiefs’ council over the affairs of individual tribes increased.
Correct. "Prior to resettlement, the chiefs’ council controlled only the broad policy of the tribal league;"
(C) The political influence of the Iroquois shamans was diminished.
The author has not discussed about shaman's political influence. The only thing the passage mentions about shaman was that they were said to have jurisdiction over religious affairs at one time.
(D) Individual tribes coalesced into the Iroquois tribal league.
We don't know when the individual tribes became united into a tribal league.
(E) The longhouse became a political rather than a religious institution.
We only know that prior settlement the long house was an institution for both political and religious issues. We have no info about the longhouse after settlement.
27. Which of the following best expresses an opinion presented by the author of the passage?
(A) Smith has overstated the importance of the political role played by Iroquois tribal chiefs in the nineteenth century.
The author mainly challenged Smith's opinon on tribal chiefs religious role, not political role. Smith believed that tribal chiefs became more active in religious issues later, while the author believed that they have been governing both political and religious issues in the longhouse before settlement.
(B) Smith has overlooked the fact that the Iroquois rarely allowed their shamans to exercise political authority.
He did not challeng Smith's view on shaman's political authority at all. It's not discussed. Not even mentioned.
(C) Smith has failed to explain why the chiefs’ council was dissolved late in the nineteenth century.
He did not challenge this point either, nor did he offer an idear himself.
(D) Smith has failed to acknowledge the role prior to the nineteenth century of the Iroquois tribal chiefs in religious affairs.
Yes. The tribal chiefs govern religious affairs in the longhouse prior to the settlement, but Smith didn't recognize that.
(E) Smith has failed to recognize that the very structure of Iroquois social institutions reflects religious beliefs.
It's out of scope. The author was not talking about social institutions.