题目

 In history, the Romany split into different groups and developed their own language, _______ there are now approximately sixty varieties.    A. by which            B. of which         C. by whom                         D. of whom 答案：B下列各项中括号里的物质是除去杂质所用的试剂，其中错误的是（　　）A．NaOH中混有Na2CO3（氢氧化钡溶液）B．CO2中混有CO（氧气）C．H2中混有HCl（NaOH溶液）D．CaCO3中混有NaCl（水）