GWD（31） 2-34

greentree_du

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

给的答案是A，我选C。求教！谢谢

carolhide

情态动词不能随意删去。

chamcham

以下是引用carolhide在2006-9-20 17:52:00的发言：

情态动词不能随意删去。

cool, that is typical NN's explanation, precise and clear