@inproceedings{rajpurkar2018squad,
 author = {Pranav Rajpurkar and Robin Jia and Percy Liang},
 booktitle = {Association for Computational Linguistics (ACL)},
 title = {Know What You Don't Know: Unanswerable Questions for SQuAD},
 url = {https://nlp.stanford.edu/pubs/rajpurkar2018squad.pdf},
 year = {2018}
}