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If ""^(n)C r denotes the numbers of com...

If `""^(n)C _r` denotes the numbers of combinations of n things taken r at a time, then the expression ` ""^(n) C_(r+1) +""^(n)C_(r-1) +2 xx ""^(n)C_r` equals

A

` ""^(n+1) C_r`

B

` ""^(n+2) C_(r+1)`

C

` ""^(n-2) C_(r+1)`

D

` ""^(n-1) C_(r+1)`

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