Complete the time traveler's frustrated diary entry.
If I _________________________ on that prehistoric butterfly during my trip to the Cretaceous period, giant intelligent hamsters _____________________________ the Earth right now!
The correct answers are hadn't stepped and wouldn't be ruling.
This is a mixed conditional connecting a past event to a present result.
We use the past perfect (hadn't stepped) for the unreal past condition (the mistake in the Cretaceous period).
We use would + base verb or would be + -ing (wouldn't be ruling) for the unreal present result (what is happening "right now").