题目

   下列说法正确的是(   ) A．KClO3和SO3溶于水后能导电，故KClO3和SO3为电解质 B．25 ℃时，用醋酸溶液滴定等浓度NaOH溶液至pH＝7，V醋酸＜VNaOH C．向NaAlO2溶液中滴加NaHCO3溶液，有沉淀和气体生成 D．AgCl沉淀易转化为AgI沉淀且Ksp(AgX)＝c(Ag＋)·c(X－)，故Ksp(AgI)＜Ksp(AgCl) 答案：DWorks which were carved on stones centuries ago are difficult ________ . [　　] A．to be read B．for reading C．to read D．for writing