题目选项分析

NASA's methodical approach to the exploration of Mars has not yet answered the questions of whether biological life forms ever emerged on Mars and, presuming such life forms to have left fossil traces to begin with, if they still exist in some moist recesses of the cold and arid planet.

NASA's methodical approach to the exploration of Mars has not yet answered the questions of whether biological life forms ever emerged on Mars and whether, presuming such life forms left fossil traces to begin with, those traces still exist in some moist recesses of the cold and arid planet.