Evolution question on speciation? Really confusing!
The answer is C

Because it explicitly tells you the fly speciates faster than the tree (1my vs 10my). That means after the extinction event, all things being equal, the fly will speciate into more niches/species in the same amount of time. While other outcomes could occur, with the information given C is by far the most likely outcome.

This is no different than a physics question asking you which of two object will reach some arbitrary marker first give two different known velocities.