请教GWD-9-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

-----------------------------------------------------------------------------------------------------------

这题我选的A。be to do 不是一定为错误形式吗？为什么选C呢？A为什么不对啊？麻烦各位帮忙分析一下。