question: What were the last names of the two people who became rivals?
context: After his share in the Farthest South achievement of the Discovery Expedition, Ernest Shackleton suffered a physical collapse on the return journey, and was sent home with the expedition's relief vessel on orders from Scott; he bitterly resented it, and the two became rivals.  Four years later, Shackleton organised his own polar venture, the Nimrod Expedition, 1907–09. This was the first expedition to set the definite objective of reaching the South Pole, and to have a specific strategy for doing so.To assist his endeavour, Shackleton adopted a mixed transport strategy, involving the use of Manchurian ponies as pack animals, as well as the more traditional dog-sledges. A specially adapted motor car was also taken. Although the dogs and the car were used during the expedition for a number of purposes, the task of assisting the group that would undertake the march to the pole fell to the ponies. The size of Shackleton's four-man polar party was dictated by the number of surviving ponies; of the ten that were embarked in New Zealand, only four had survived the 1908 winter.Ernest Shackleton and three companions (Frank Wild, Eric Marshall and Jameson Adams) began their march on 29 October 1908. On 26 November they surpassed the farthest point reached by Scott's 1902 party. "A day to remember", wrote Shackleton in his journal, noting that they had reached this point in far less time than on the previous march with Captain Scott. Shackleton's group continued southward, discovering and ascending the Beardmore Glacier to the polar plateau, and then marching on to reach their Farthest South point at 88°23'S, a mere 97 nautical miles (180 km; 112 mi) from the pole, on 9 January 1909. Here they planted the Union Jack presented to them by Queen Alexandra, and took possession of the plateau in the name of King Edward VII, before shortages of food and supplies forced them to turn back north. This was, at the time, the closest convergence on either pole. The increase of more than six degrees south from Scott's previous record was the greatest extension of Farthest South since Captain Cook's 1773 mark. Shackleton was treated as a hero on his return to England. His record was to stand for less than three years, being passed by Amundsen on 7 December 1911.
answers.text: Scott Shackleton