题目

In the birthday party, Mary can’t wait to open the presents. A．wants to wait for the presents             B．wants to open the presents very much C．can’t wait for the presents                  D．don’t want to open the presents 答案：B下列说法正确的是（　　）A．两难溶电解质作比较时，Ksp小的，溶解度一定小B．欲使溶液中某离子沉淀完全，加入的沉淀剂应该是越多越好C．所谓沉淀完全就是用沉淀剂将溶液中某一离子除净D．欲使Ca2+离子沉淀最完全，选择Na2CO3作沉淀剂效果比Na2SO4好