张师傅要为三位客户安装洗衣机，来去时间在内，王家需要20分钟，赵家需要40分钟．李家需要30分钟．要使三位客户安装和等候的时间总和最少，请你帮张师傅合理安排一下安装顺序．

Battens are fitted in cargo holds across the frames of the vessel from the turn of the bilge upward. The purpose of these cargo battens is（）.

A.for securing a snatch block when snaking cargo into the wings of the hold

B.to prevent cargo from coming in contact with the vessel's frames or shell plating

C.tp prevent fittings to which cargo lashing may be secured

D.to support the dunnage floors which are laid down between tiere of cargo