A、It has lost its primary oxygen sources. B、It has lost its backup oxygen sources. C、It has lost both the primary and the backup

The U.S. Space Agency NASA says Russia’s orbiting Mir space station has lost its primary and backup oxygen sources. If the problem is not fixed, the 3-member crew would have to abort the mission. But, a Russian space official in Moscow told Reuters News Agency that only the primary generator developed trouble and that the unit was repaired by the crew. More about the latest problem on board the space station from VOA’s Nick Simming.
   "The U.S. Space Agency says Mir’s two primary sources of oxygen have stopped working and now there is only sever- al day’s supply of oxygen inside Mir’s cabin. Mir’s backup oxygen generating candles failed Monday just after the normal oxygen supply system used by the spacecraft unexpectedly shut down. That normal oxygen source, a method that extracts oxygen from water, had been turned off for several days to conserve energy heated and automatically shut down. NASA’s spokesman Michael Brock Hais says if Mir’s oxygen supply problem is not fixed soon, the two Russians and one American on board will have to abort. This problem is the most serious to plague the space station which has endured power loss, computer malfunction and even a collision with a supply vessel all in the past six months. Nick Simming VOA News, Washington."