题目

下列各组括号内除杂的方法或试剂错误的是                            A． Cu粉中混有Fe粉（用磁铁吸引）     B．Cu粉中混有CuO（稀硫酸） C．CO中混有CO2 （氢氧化钠溶液）      D．CO2中混有CO（点燃） 答案：DI ______ in the hospital yesterday. I had to look after my sick mother. A．am              B．was              C．are              D．were