求助：涛涛GWD31－02－34

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.

1. and whether, presuming such life forms having left fossil traces to begin with, those traces can
2. and whether, if it is presumed that such life forms left some fossil traces to begin with, can those traces
3. and whether, presuming such life forms left fossil traces to begin with, those traces
4. and, presuming such life forms did leave some fossil traces to begin with, if they can
5. and, presuming such life forms to have left fossil traces to begin with, if they

答案是A。我选的是C，having left 的形式不对吧，是因为情态动词can吗？

查过老贴，但没有结果，麻烦哪位高人帮帮我吧～

3x!

此题经过讨论答案不是C吗？怎么变成A了？