Task: Question Answering
Input (English): Thus we consider the task of answer generation for TweetQA and we use several standard metrics for natural language generation to evaluate QA systems on our dataset, namely we consider BLEU-1 BIBREF16 , Meteor BIBREF17 and Rouge-L BIBREF18 in this paper. 
 Question: What evaluation metrics do they use?
Output (English): BLEU-1 Meteor  Rouge-L