###INSTRUCTION: Make the sentence fluent: downoff example, Northern Nigeria were still one of the only part of the world that the Polio virus continues to be prevalent.
###RESPONSE: 
For example, Northern Nigeria is still one of the only parts of the world in which the polio virus continues to be prevalent.
down-off example, Northern Nigeria was still one of the only parts of the world that the Polio virus continued to be prevalent.