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.
A) and whether, presuming such life forms having left fossil traces to begin with, those traces can
B)
and whether, if it is presumed that such life forms left some fossil traces to begin 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
Key: A
为什么C不好, A 与C的区别在于 having 和 can，having left, left 有什么区别呢？ | 
