Which word in this sentence is an adverb, and what information does it provide?

The British soon made Australia a prison colony.

However, the idea of real-life people living in what would become the united states for thousands of years before columbus ever left spain never dawned on me. what would be the best way to revise this sentence for greater clarity? a) however, the fact that columbus left spain thousands of years after people settled what would become the united states never dawned on me. b) it never dawned on me, however, the idea of real-life people living in what would become the united states for thousands of years before columbus ever left spain. c) however, the fact that people were already living in what would become the united states for thousands of years before columbus ever left spain never dawned on me. d) however, the idea never dawned on me that long before columbus ever left spain, real-life people lived for thousands of years in what would become the united states.

Urgently need to do with 1-20. you very much!

How does tiresias prophecy affect the plot of the story ?