[单选题]
A boat can travel 4.0 m/s in still wax m-) r7:f o e+o: lieaytj5xl k;/tuw(25wlqater. With what speed, relru;qwgd 37vsq5 b/pfpg 3q0zs36id :p ative to the shore, do3qwq;ppd s 3s i gf/z:ug5073dpvqr b6es it move in a river that is flowing at 1.0 m/s if the boat is heading downstream?
