For the human evaluation, we follow the standard approach in evaluating machine translation systems BIBREF23 , as used for question generation by BIBREF9 . We asked three workers to rate 300 generated questions between 1 (poor) and 5 (good) on two separate criteria: the fluency of the language used, and the relevance of the question to the context document and answer. 
 Question: What human evaluation metrics were used in the paper?
rating questions on a scale of 1-5 based on fluency of language used and relevance of the question to the context