[单选题]
A polar bear starts at the North Pole. Itt3 d 3z 4k -qnz,y/awek;ffl9 .kasji0 trae.i6mh zc,s xtdu );f4vels 1.0 km south, then 1.0 km east, then 1.0 km north, theh6 d; x.s tecz,4f)umin 1.0 km west to return to its starting point. This trip takes 45 min. What was the bear's average speed?
