In 1997, a group of twenty British women made history. Working in five teams with four women in each team, they walked to the North Pole. Apart from one experienced female guide, the other women were all ordinary people who had never done anything like this in their lives before. They managed to survive in an environment which had defeated several very experienced men during the same time period.               The women set off as soon as they were ready. Once on the ice, each woman had to ski along while dragging a sledge weighing over 50 kilos. The temperature was always below the freezing point and sometimes strong winds made walking while pulling so much weight almost impossible. It was also very difficult for them to put up their tents when they stopped each night. In such conditions, the women were making good progress if they covered fourteen or fifteen kilometers a day. But there was another problem. Part of the journey was across a frozen sea with moving water underneath the ice and at some points the team would drift back more than five kilometers during the night. That meant that after walking in these very severe conditions for ten hours on one day, they had to spend part of the next day covering the same ground again. Furthermore, each day it took three hours from waking up to setting off and another three hours every evening to set up the camp and prepare the evening meal.               So, how did they manage to succeed? They realized that they were part of a team. If any one  of them didn't pull her sledge or get her job done, she would endanger the success of the whole expedition.  Any form of selfishness could result in the efforts of everyone else being completely wasted, so personal Feelings had to be put on one side. At the end of their journey, the women agreed that it was mental effort far more than physical fitness that got them to the North Pole. It was difficult for the women to cover 15 kilometers a day because   _  .
they got too tired the ice was moving they kept getting lost the temperature were too low