[单选题]
A polar bear starts at the North Pole. It travels 1lx w sw28dtsgy; w35.o.0 km south, then 1.0g*hmjir6c8,/i :otls km east, then 1.0 km north, then 1.0 km west to return to its starting point. This trip r/t: j hlc6m*gs ,ii8otakes 45 min. What was the bear's average speed?
