题目

 在电解水制取H2和O2时，为了增强溶液的导电性，常加入一些电解质。下列物质中最合适的是 A．Na2SO4 B．CuC12     C．NaCl   D．AgNO3 答案：A She didn't know ________． [　　] A．who he was looking after B．who was he looking for C．who he is looking for D．who he is looking after