Which of the following is a true statement about the map?
A. The border between Washington and Oregon is a thin, black line this indicates a national boundary.

B. The border between lowa and Nebraska is a thin, blue line this indicates a natural river boundary.

C. The border between Mexico and Texas is a thick, black line; this indicates a state boundary.

D. The border between Canada and the United States is a thin, black line, this indicates a national boundary.