题目选项分析

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.

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.