[单选题]
A boat can travel 4.0 m/s in s6 fps zhas7am,ek9l dw64 .)dxtill water. Withndr6n -os3kzykss: d4get*f,w 9 4 w2s what speed, relative to the shore, does it move in a river that is flowing at 1.0 m/s if the boat is heading straight across the te6ddw sr 3:s-s2 4nk 4*gykszw9f n,oriver?
