Learning to Ask Unanswerable Questions for Machine Reading Comprehension Haichao Zhu author Li Dong author Furu Wei author Wenhui Wang author Bing Qin author Ting Liu author 2019-07 text Proceedings of the 57th Annual Meeting of the Association for Computational Linguistics Anna Korhonen editor David Traum editor Lluís Màrquez editor Association for Computational Linguistics Florence, Italy conference publication zhu-etal-2019-learning 10.18653/v1/P19-1415 https://aclanthology.org/P19-1415/ 2019-07 4238 4248