题目

某溶液中存在Mg2＋、Ag＋、Ba2＋三种金属离子，现用NaOH、Na2CO3、NaCl三种溶液使它们分别沉淀并分离出来，要求每次只加一种溶液，滤出一种沉淀，所加溶液顺序正确的是( )     A．Na2CO3 NaCl NaOH                B．NaOH NaCl Na2CO3     C．NaCl NaOH Na2CO3                        D．NaCl Na2CO3 NaOHHe speaks Chinese with a foreign accent. Sometimes the class ________ understand what he is saying.A.doesn'tB.isn'tC.don'tD.aren't