...or shall I say To pass the impassable ice ridges?
This is the full text offered as an open cloze in Use of English:
'"In 1914, Ernest Shackleton, the famous polar explorer, headed towards Antarctica in the Endurance. He and his twenty-eight companions intended to cross Antarctica on foot.
"However, their ship became stuck in the ice, and, although it had been built for these conditions, was slowly crushed by the pressure of the ice. It was not possible for Shackleton and his men to travel over the frozen sea to the nearest land, four hundred kilometres away, because the ice was not flat and smooth. It was raised up into high ridges which / that were often impassable. Moreover, the ice was breaking / broken up into large pieces which moved according to the wind and current.
"During their six months on the ice, Shackleton's men survived by eating their dogs, and penguins and seals if / when they could catch them. Eventually, they reached Elephant Island, which was uninhabited. In a small boat they had taken from the ship, Shackleton and six of his men sailed for over eight hundred miles to another / an island where they knew there was a whaling-station, and therefore food, shelter and a radio. Their boat landed on the wrong side of the island and they had to climb a mountain range and march sixty kilometres to safety. Shackleton then arranged for a ship to collect his twenty-two companions on Elephant Island.
"It is because of his superb powers of organization and leadership that all his men survived this terrible experience.'"