Because of the barrier of ice to the east, the Pacific Ocean to the west, and populatedareas to the north, there may have been a greater impetus for people to move in a southerly direction.
因为东面有冰的屏障，西面是太平洋，而且北面是人口稠密的地区，所以促使人们向南迁移的动力会更大。
2
Many jet ski riders are big show-offs who stick around populatedareas so everyone can see their turns and manoeuvres.