A、He was seriously injured. B、His helmet was found leaking. C、His spaceship was lacking in fuel. D、He was running short of water

National Aeronautics and Space Administration (NASA) has ended the spacewalk involving UK astronaut Tim Peake after his US colleague reported water in his helmet. Tim Kopra reported a small amount of water, but the flight director took the precaution of ending the event early. The agency is under a ruling to terminate a spacewalk under such circumstances after an incident in 2013, when a European astronaut developed a significant helmet leak. The astronauts were outside the space station for four hours 43 minutes. The main objective of the spacewalk— replacing a failed electrical box— had already been completed. Just before 17：00 GMT, Colonel Kopra, a NASA astronaut who is a veteran of two spacewalks, told mission controllers a water globule measuring a few inches across had developed inside the helmet. He was able to sample the water and found it was cold, which is indicative of a leak from part of the US-built suit’s cooling system.
1. Why did Tim Peake end his spacewalk early?
2. What is the main task of this spacewalk?