题目2.[单选题]实级数-|||-∑bn-|||-n-1-|||-都收敛是复级数-|||-sum _(n=1)^infty ((a)_(n)+i(b)_(n))-|||-收敛的-|||-条件-|||-bigcirc A.充分-|||-bigcirc B.必要-|||-bigcirc C.充分且必要-|||-bigcirc D.非充分也非必要题目解答答案