Detailed Instructions: Given a disfluent sentence, modify the sentence to it to its equivalent fluent form, preserving the meaning of the sentence.
See one example below:
Problem: Who did the Han Chinese want to help the Khitan no I mean the Mongols fight?
Solution: Who did the Han Chinese want to help the Mongols fight?
Explanation: The input initially means Khitan and then changes to Mongols, hence this is correct.

Problem: In what year did or instead how old are the gravestones that reference the plague?
Solution:
How old are the gravestones that reference the plague?