The function f(z) of complex variable z = x + iy, where \(i = \sqrt { - 1} ,\) is given as f(z) = (x3 – 3xy2) + i v(x,y). For this function to be analytic, v(x,y) should be

• A. (3xy2 – y3) + constant
• B. (3x2y2 – y3) + constant
• C. (x3 – 3x2y) + constant
• D. (3x2y – y3) + constant