A

$\displaystyle\sum\limits_{n=1}^{\infty}(-1)^n\dfrac1{\sqrt n}$

B

$\displaystyle\sum\limits_{n=1}^{\infty}(-1)^n\dfrac{3^n}{2^{2n}}$

C

$\displaystyle\sum\limits_{n=1}^{\infty}(-1)^n\dfrac{n+1}{2n-1}$

D

$\displaystyle\sum\limits_{n=1}^{\infty}(-1)^n\dfrac n{\sqrt{2n^2-1}}$