Two discrete time systems with impulse responses $h_t[n]=\delta[n-1]$ and $h_2[n]=\delta[n-2]$ are connected in cascade. The overall impulse response of the cascaded system is

- $\delta[n-1]+ \delta[n-2]$
- $\delta[n-4]$
- $\delta[n-3]$
- $\delta[n-1] \delta[n-2]$