[单选题]
A boat can travel 4.0 m/s in stilsf:wxlsb-,k+4,xn e w t(mwm -l water. With what speed, relativbw ; qe3ap*3i m;h1ywwe to the shore, does it move in ah3ywep1; iw * 3;qbwma river that is flowing at 1.0 m/s if the boat is heading straight across the river?
