Harry has been out of work for six months, so he has difficulty _____.

A．earning livings

B．earning his living

C．to earn livings

D．to earn his living

进口货物报关单付汇证明联是海关对已办理进口申报的货物所签发的证明文件，是银行和国家外汇管理部门办理售汇、付汇及核销手续的重要依据之一。 ( )