If $\mathrm{N}>\mathrm{n}>1$, then the value of $\sum_{\lambda=0}^{\mathrm{N}}{ }^{\lambda+\mathrm{n}-1} \mathrm{C}_{\mathrm{n}-1}$ is equal to
(a) 1
(b) ${ }^{\mathrm{N}} \mathrm{C}_{\mathrm{n}+1}$
(c) $\mathrm{N}+\mathrm{n} \mathrm{C}$
(d) ${ }^{N+n-1} C_{n-1}$