[单选题]
A polar bear starts at theznye ,zi) hrzh/f* ;+c Nortv*0qd ;es.u v7 foyb+gh Pole. It travels 1.0 km south, then 1.0 km east, then 1.0 km north, then 1.0 km west 0b v eoq *vs7;g.df+uyto return to its starting point. This trip takes 45 min. What was the bear's average speed?
