[单选题]
A boat can travel 4.0 m/s /4f3mjt5 iudm/w 4pko;mr8 wc s 4g -(/dw n/una;ia.kv:tibmgdm-i1in still 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 downwt/i( ;m a-miv b-usnd:ag14i .nkgd/stream?
