If ""^(n)C(r) denotes the number of comb...

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

A

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

B

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

C

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

D

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

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The correct Answer is:

B

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