题目

I’m sure that middle school students will benefit _______taking exercise every day, which is ______ great benefit ____ their health.    A.by; of; at       B.from; of; to      C.from; by; to         D. by; from; at 答案：B下列各离子方程式中，属于水解反应的是A．HCO3-+H2OH3O++CO32-            B．NH4++H2ONH3·H2O+H+C．PO43-+H3O+HPO42-+H2O                    D．H2O+H2O H3O++OH-