This question asks us to articulate the main (central) purpose of a particular segment of this passage--specifically, Lines 11-14. Let's first review those lines:
"But this decision has placed on provincial courts the enormous burden of interpreting and translating the necessarily general constitutional language into specific rulings."
Answer choice (D) says that this passage's "main purpose" is "to describe one aspect of the *process by which* constitutional reforms are enacted in Canada." This is not right--nothing about these lines tells us anything about *how* (the process by which) constitutional reforms are enacted. Rather, these lines tell us one *consequence* of the constitutional reforms, once they've already been enacted.
By contrast, answer choice (B) says that the "main purpose" of these lines is "to locate the source of a systemic problem in protecting aboriginal rights in Canada." This is correct--the decision (of the federal government to extend constitutional protection to certain aboriginal rights) has led to a systemic problem (that is, it has forced provincial courts to interpret and translate "necessarily general constitutional language").
Hope this helps to clarify. Please let us know if you have any additional questions!
