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If n is any positive integer then 1/1.3+1/3.5+1/5.7+.....+1/(2n-1)(2n+1)=
Difficulty: Easy
A: 
n/4(n+1)
B: 
$\frac{n^{2}(n+1)^{2}}{4}$
C: 
n/2n+1
D: 
$\frac{n^{2}}{2n+1}$