[单选题]
A boat can travel 4.0 m/s in still wa7xv8zp7d + sn6au oeuh )nri3rahw:6-ter. 3diu(f h2jx;a9)9t ps1x synj With what speed, relative to the shore, does it move in a river that dj9(1;hn2yx x 9t uiasspj)f3is flowing at 1.0 m/s if the boat is heading upstream?
