题目

He has changed a lot. He is not what he was used to be. 答案：去掉 was，used to 表示今昔对比 解析: be used to 表示“习惯于”。用一种试剂鉴别浓硝酸、浓硫酸和稀硝酸、稀硫酸，所用的试剂是________，有关的反应方程式___________、____________、___________．