GWD 19-27 If it were to...

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.  

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1. and, if it strikes Earth, it can do tremendous damage to part of the planet but>>
   
2. and, if it would strike Earth, part of the planet could experience a tremendous amount of damage but it would>>
   
3. and that, if it were to strike Earth, could do tremendous damage to part of the planet but would:
   
4. and that, if Earth is struck by it, can do part of the planet tremendous damage, but it would: it no zhidai >>
   
5. and that, if it strikes Earth, it could experience a tremendous amount of damage but : experience awkward

做题的时候选对了，现在看的时候又糊涂了

我记得og 上有 if 的考点，都是考：if  x happens, then y will happen. or y will happen only if x happens. IF 句子跟的总是现在时，上题中用了 WERE TO 结构，我忘了 WERE TO 这个语法点了，也没查到，还请大家帮忙，这里是不是因为是个ASSUMPTION，所以用了虚拟？

我看到的IF WERE TO 的结构有： If I were the priminister, or If  you were president. 说明都是不现实的东西，而这里科学家have identified .也适用虚拟马？

谢谢