Q27:
Scientists have identified an asteroid, 2000 BF19, that is about half a mile wide and, if it strikes Earth, it can do tremendous damage to part of the planet but probably not cause planetwide destruction.
A. and, if it strikes Earth, it can do tremendous damage to part of the planet but
B. and, if it would strike Earth, part of the planet could experience a tremendous amount of damage but it would
C. and that, if it were to strike Earth, could do tremendous damage to part of the planet but would
D. and that, if Earth is struck by it, can do part of the planet tremendous damage, but it would
E. and that, if it strikes Earth, it could experience a tremendous amount of damage but
看过以前的贴子,没有答案,我想问THAT 在这句话里是什么成分,如果是定语修饰asteroid, 2000 BF19,为什么不用WHICH?或者THAT 是其它什么成分? 另外此句一定要用虚拟语气吗? | 
