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 planet wide 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
答案：C 语法笔记里面是从虚拟语气的角度解答这题的，其实可以从主语的重复解答这题，而且非常简单。 That在这里指代asteroid，做定语从句的主语，那么从句中就不能出现别的主语 A中出现了it；B中出现了part of the planet；C正确；D中出现了it；E中出现了it。