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
Beginning a Bargain-Basement
Invasion of Mars
Eventual objectives are to return samples of rock and soil, perhaps by
2008, and someday send astronauts for a long visit. Behind this
methodical approach is the enduring question of whether life ever
emerged on Mars and left some fossil traces, and whether it still exists in some
moist
recesses of this cold, arid world.
可是后面的结构，变动很大。
我支持C。虽然还是讲不太出来可信服的原因。
从原文emerged/exists的时态可以看出，采用的是事件记述的方法，无感情色彩吧？
still exist仍然存在与can still exist依然能（这里就在强调能不能，的这种生存能力）存在，体会起来还是有点小区别吧？
等待牛牛们来验证
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