[单选题]
A polar bear starts at the North Pole. Izth;y q9oh3d 1t travels 1vtbo xklz67/4lo )1xw.0 km south, then 1.0 km east, then 1.0 km north, then 1.0 km west to return to its starting p1z 4xv7/l klotw)6box oint. This trip takes 45 min. What was the bear's average speed?
