[单选题]
A boat can travel 4.0 m/s in stiu n/a/ kdz 2i5 6lte5xpc-fl+pll water. With what speed, relats1mj ) axk+mu2(/iva kive to the shore, does it move in a river th)i k(+mus /mavkjax12 at is flowing at 1.0 m/s if the boat is heading straight across the river?
