题目

 I began watching here an hour ago, but now nothing________ yet. A. happens  B. will happen   C. happened  D. has happened 答案：D19．生产中通常用铁制容器盛装下列哪一溶液？（　　）A．氯化铜溶液B．稀硫酸C．浓盐酸D．浓硝酸