Let's break down the sentence in question:

"This pragmatic approach" refers to the preceding sentence: "What constitutes an American Indian reservation is a question of practice, not of legal definition, and the pueblos have always been treated as reservations by the United States." In other words, it is pragmatic to define a piece of land as a reservation based on how the land has been treated in practice, rather than just by legal definition.

The pragmatic approach described above is buttressed (or supported) by a court case, Arizona vs. California. In this case, "the Supreme Court indicated that the manner in which any type of federal reservation is created does not affect the application to it of the Winters doctrine." This means that the Winters doctrine can be applied to a piece of land that became a reservation through legal rulings, through its historical treatment as a reservation, or by any other means.

Let me address this question specifically:

The Winters doctrine did not create any reservations -- it merely established that an existing reservation had the "right to use waters flowing through or adjacent" to the land. It established this right despite the fact that water was not discussed in the original treaty to create the reservation. According to the passage, later court cases expanded the Winters doctrine to apply to more diverse situations.

Arizona vs. California was another of these cases that applied the Winters doctrine to a broader range of situations than did the Winters Vs. United States case. That's why (B) is the best answer choice for question #5.
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