Let R be set of points inside a rectangle of sides a and b (a, b > 1) with two sides along the positive direction of x-axis and y-axis. Then
A. R = {(x, y) : 0 ≤ x ≤ a, 0 ≤ y ≤ b}
B. R = {(x, y) : 0 ≤ x < a, 0 ≤ y ≤ b}
C. R = {(x, y) : 0 ≤ x ≤ a, 0 < y < b}
D. R = {(x, y) : 0 < x < a, 0 < y < b}