(B) says, "a common-sense interpretation of the phrase 'within living memory'"
The problem with (B) is that although it may seem like common sense, the passage never says that the court relied upon a common-sense interpretation. so this is why we can get rid of (B).
(E) says, "testimony establishing certain historical facts"
The 1991 case is the one in which Marina Katelnikoff joined Boyd Dickinson and the court overturned the previous decision. The passage notes in lines 41 and 42 that testimony from Alaska natives was a part of the case, so (E) has textual support and is the correct answer choice.
Does this make sense? Let us know if you have any other questions!