question_answer

If n and r are two positive integers such that \[n\ge r,\]then\[^{n}{{C}_{r-1}}{{+}^{n}}{{C}_{r}}\]is equal to:

A)  \[^{n}{{C}_{n-1}}\]                        

B)                         \[^{n}{{C}_{r}}\]

C)                         \[^{n-1}{{C}_{r}}\]                         

D)                         \[^{n+1}{{C}_{r}}\]

E)                         \[^{n-1}{{C}_{r-1}}\]