8.下列级数为收敛级数的是 ()-|||-https:/img.zuoyebang.cc/zyb_680ed4fad55f91a10b127dfe4bfe61ac.jpg+dfrac (1)(2)+dfrac (1)(3)+dfrac (1)(4)+... +dfrac (1)(n)+... -|||-B dfrac (1)(2)-dfrac (2)(3)+dfrac (3)(4)-dfrac (4)(5)+... +((-1))^n-1dfrac (n)(n+1)+... -|||-C 1/(√2-1)-√ dfrac (1)(2+1)+dfrac (1)(sqrt {3)-1}-dfrac (1)(sqrt {3)+1}+dfrac (1)(sqrt {4)-1}-dfrac (1)(sqrt {4)+1}+... +dfrac (1)(sqrt {n)-1}+dfrac (1)(sqrt {n)+1}+... +-|||-D 1/2 + dfrac (1)(6)+dfrac (1)(12)+dfrac (1)(20)+... +dfrac (1)(n(n+1))+...