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.

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.

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.

This sentence has the most clarity because none of the pieces interrupt another. It begins with the transition that shows what follows is a change. The next piece is the narrator talking about the idea that never dawned on her. By having this part first, we know that the information that follows is the idea that never entered her mind until now. Then the idea follows. In option C the idea statement is interrupted by the actual idea. In option B the idea statement is interrupted by however. Option A has the idea statement after the entire rest of the sentence which also doesn't work for clarity.