Consider a six-point decimation-in-time Fast Fourier Transform (FFT) algorithm, for which the signal-flow graph corresponding to X[I] is shown in the figure. Let $${W_6} = \exp \left( { - \frac{{j2\pi }}{6}} \right).$$    In the figure, what should be the values of the coefficients a₁, a₂, a₃ in terms of W₆ so that X[I] is obtained correctly?

A. $${a_1} = 1,{a_2} = W_6^2,{a_3} = {W_6}$$

B. $${a_1} = - 1,{a_2} = W_6^2,{a_3} = {W_6}$$

C. $${a_1} = - 1,{a_2} = {W_6},{a_3} = W_6^2$$

D. $${a_1} = 1,{a_2} = {W_6},{a_3} = W_6^2$$

Answer: Option D