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 having left fossil traces to begin with, those traces can still exist in some moist recesses of the cold and arid planet.
- and whether, presuming such life forms having left fossil traces to begin with, those traces can
- and whether, if it is presumed that such life forms left some fossil traces to begin with, can those traces
- and whether, presuming such life forms left fossil traces to begin with, those traces
- and, presuming such life forms did leave some fossil traces to begin with, if they can
- and, presuming such life forms to have left fossil traces to begin with, if they
涛涛31的答案是a，但是我记得白勇在语法里讲过不能用having done做定语修饰名词，所以a应该不对。另外，从逻辑上讲，question的应该是这些traces是否存在，而不是他们能否存在，所以我觉得应该选C。 | 
