---What did you look for me for, Mary?

--- The boss wondered where you ___________ and how long you __________ there.

A．had been, had been

B．had gone, had gone

C．had been, had gone

D．had gone, had been

随着人们生活质量的不断提高，废电池必须进行集中处理的问题被提到议事日程，其首要原因是 [ ]

A．利用电池外壳的金属材料

B．防止电池中汞、镉和铅等重金属离子对土壤和水源的污染

C．不使电池中渗泄的电解液腐蚀其他物品

D．回收其中石墨电极