Consider a discrete-time accumulator system \(y\left[ n \right] = \mathop \sum \nolimits_{k = - \infty }^n x\left[ k \right]\) and the backward difference system y[n] = x[n] – x[n – 1] where x[⋅] represents the input and y[⋅] represents the output of the individual systems.When these two systems are cascaded as in the figure, the impulse response of the combined system with output z[n] is

• A. Unit impulse sequence
• B. Unit step sequence
• C. Unit ramp sequence
• D. None of the above