be to do一定错么？

任何语法都没有一定错的

be to do

1.表示很快发生的动作

2.表示没有计划,随即发生的动作

3表示主观,不能用于客观的将来

这个be to do确实很矛盾，

GWD-9-27正确答案里：

Scientists have identified an asteroid, 2000
   BF19, that is about half a mile wide and that, if it were to strike Earth, could do tremendous damage to part of the planet but would probably not cause planetwide destruction.

就对了，并且明确表示”if it were to strike Earth用了正确的语态“。

但是OG里有一题出现which非限定修饰的选项矛盾时，ETS又用”be to do是错误用法“来排除了一个其他方面看起来对的选项