[单选题]
A boat can travel 4.0 m/s in.zi2 o a0h8;pjgcp.gyl9a4p1 zg j j(u sti4jn09;pybg 3cnkq t9x vu:y2 zll water. With 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 r9u ynq2zt:; 0cv g3npxj9bky4iver?
