Let S denotes the infinite sum $$2 + 5x + 9x^2 + 14x^3 + 20x^4 + ...$$ , where |x| < 1 and the coefficient of $$x^{n - 1}$$ is n( n + 3 )/2 , ( n = 1, 2 , . . . ) . Then S equals:

A

$$(2-x)/(1-x)^3$$

B

$$(2-x)/(1+x)^3$$

C

$$(2+x)/(1-x)^3$$

D

$$(2+x)/(1+x)^3$$