Geometric boundaries are especially common in A.
former colonies, because geometric boundaries can be negotiated without traveling to the location.

B.
non-self-governing territories, because geometric boundaries can effectively reinforce cultural boundaries.

C.
island states, because geometric boundaries can effectively reinforce physical boundaries.

D.
states bordering rivers, because rivers tend to shift their courses slightly over time, requiring oversight.

E.
regions with impassable mountain ranges, because this inaccessibility makes them poor boundaries.