Editor
$^{n-1}C_{r}+^{n-1}C_{r-1}$=
Difficulty: Easy
A: 
$^{n-2}C_{2r-1}$
B: 
$^{2n-2}C_{2r-1}$
C: 
$^{n}C_{r}$
D: 
$^{n-2}C_{r}$
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