一道没编号的题，大家帮忙看一下

NASA's methodical approach to the exploration of Mars has not yet answered the question of whether biological life  forms ever mergerd 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.

B. and whether, if it is pressumed that such life forms left some fossil to being with, can those traces

C. and whether, presuming such life forms left fossil traces to begin with, those traces

D. and, presuming such life forms did leave some fossil traces to begin with, if they can

E. and, presuming such life forms to have left fossil traces to begin with, if they

D，E肯定不对了，但 ABC 里选哪个呢？？

谢谢楼上兄弟的解释~

但 A的 having left 的用法怎么解释呢？