19.已知 (BaS(O)_(4))=1.07times (10)^-10 , (BaC(O)_(3))=2.58times (10)^-9 ,在1LNa2 CO3溶液中,转-|||-0.020molBaSO4固体.问此Na2CO3溶液的最初浓度为多少:-|||-A. .254molcdot (L)^-1 B. .244molcdot (L)^-1 C. .488molcdot (L)^-1 D.0.508mol·L^(-1)