I think it is B, that helps disprove it so it can't prove it.
Fish will eat tadpoles if they can get to them. The only way to stop them would be to give the tadpoles a space that the fish can't get to, like a shallow area with a barrier (plastic mesh would work but make sure the fish can't get caught in it) or lots of plants, or make a separate wildlife pond.
B) Oxygen may not have been able to accumulate in the atmosphere
When researchers create lesions, they are destroying a piece of the brain.
