[单选题]
A swimmer heading direct)hf9hgm 2ib7,uk+i3ft ec2vg ly across a river60 jb )4mlwggt7n5x/1:t swj u0 npadp 200 m wide reaches the opposite bank in 6 min 40 s. She is swepj6nu7pjsb50 :/ t0awtp4g1w x)l gdnmt downstream 480 m. How fast can she swim in still water?