小白一枚、求大侠相助GWD

ilo061124

Q6 :TT-GWD 2-34.

NASA’s methodical approach to theexploration of Mars has not yet answered the questions of whether biologicallife forms ever emerged on Mars and whether, presuming such life formshaving left fossil traces to begin with, those traces can still exist insome moist recesses of the cold and arid planet.

A.      and whether, presumingsuch life forms having left fossil traces to begin with, those traces can

B.      and whether, if it ispresumed that such life forms left some fossil traces to begin with, can thosetraces

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

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

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

请问黄色区域的意思如何理解啊?结构如何啊 ？百思不得其解。。。。尤其是那个left

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黄色在哪里呀~黄色在哪里？