Sentence Correction (SC) | Re: For the first time in the modern era, non-Hispanic Whites are official

I need help understanding the prepositional phrase in choice D - "down from nearly three-quarters a decade ago" - what is this modifying "a little less than half the population of the state"?

In general if you have a [clause] + [participle phrase] + [prepositional] what does the prepositional phrase modify?

---