Not supported, because the author doesn’t suggest that decisions “rarely” meet the goals of constitutional reforms. The decisions may be inconsistent, but that doesn’t imply that they usually don’t conform to the constitutional reforms’ goals. Because (A) isn’t supported, it can’t be the purpose of the line.

This best capture the author’s purpose in the sentence, which is to describe why it’s been difficult to consistently recognize and enforce aboriginal rights.

The constitutional reforms were already enacted in 1982. The problem relates to interpreting the constitutional reforms, not in getting the reforms enacted.

The sentence doesn’t have anything to do with the process of enacting reforms.

The author doesn’t criticize the use of general language. Notice that she says the language is “necessarily” general; that means it must be general. So, although the author does believe the general language creates problems, that doesn’t imply the author thinks the general language should be changed or should be made more specific.