A fault opens in a forest and separates a population of lizards in half. In 100 years the fault closes and the lizards can interact again. Explain why the lizards are no longer able to breed.

An answer deserving full marks would be a clearly written, long-form paragraph containing 4-5 of these points:
The lizard populations cannot interact or share genes after the faultThe two sides of the fault have different environmentsThe two populations have different selection pressuresThe separate populations thus evolve different adaptations to surviveWhen they reconnect their genes are too different to breed viablyThey have become two separate species