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If n is any positive number, then 1/2.4+1/4.6+1/6.8+......+1/2k(2k+2)=
Difficulty: Easy
A: 
n/2n+1
B: 
n/4(n+1)
C: 
$\frac{n^{2}(n+1){2}}{4}$
D: 
$\frac{2n^{2}+4}{4}$