The Z-Transform X(z) of a discrete time signal x(n) is defined as ____________

• A. ( sum_{n=- infty}^{ infty}x(n)z^n )
• B. ( sum_{n=- infty}^{ infty}x(n)z^{-n} )
• C. ( sum_{n=0}^{ infty}x(n)z^n )
• D. None of the mentioned