Potential at point B with respect to A = 1.5v
Potential at point C with respect to A = 3v
Potential at point D with respect to A = 1.5v [because (+1.5) + (+1.5) + (-1.5v)]
Potential at point C with respect to B = 1.5v
Potential at point C with respect to D = 1.5v
Potential at point A with respect to B = -1.5v
Potential at point A with respect to C = -3v
Potential at point A with respect to D = -1.5v [because (-1.5) + (-1.5) + (+1.5v)]
Potential at point B with respect to C = -1.5v
Potential at point D with respect to C = -1.5v
Potential at point B with respect to D = 0v [because (+1.5v) + (-1.5v)]