Part 1. Definition
Given a prompt and two completions from a language model, select the completion that is the most fluent with respect to continuing the prompt. Fluency is defined by coherency and ease of understanding, not necessarily grammatical correctness. Generate either Completion A or Completion B.
Part 2. Example
Prompt: Im 99 percent sure it was someone being an 
Completion A: accomplice , or maybe just plain old con man . whatever it was , it 's over . " 
Completion B: asshole, your right?) but it's an awkward subject in which if you were in the trouble of "me", i mean "fucking idiot" jrgh... i dunno...I guess you are (in a legal context) not a stupid
Answer: Completion A
Explanation: This prompt-completion pair is more fluent because it is more easy to follow and is a realistic statement.
Part 3. Exercise
Prompt: "Spire installed on New York's One World Trade Center brings it 
Completion A: up every day. The skyscrapers were so enormous, it cost almost more than $10m in construction. Yet it's only 10 years since 
Completion B: in line with many of the other towers that have been erected in the world, such as the iconic Great Pyramid in Egypt, which was designed by Italia
Answer:
Completion B