–What do you think of your job, Bob?

–Though ____ flexibility, it is a job____ you are doing something serious but interesting.

A．lacking; where

B．lacking of; which

C．lacking in; when

D．lacking; that

凡是列入国家工业产品生产许可证目录、铁路行政许可目录、（）内的铁路专用设备，施工单位在采购时，应要求取得相应的许可或认证。