Multi-step Entity-centric Information Retrieval for Multi-Hop Question Answering. - Rajarshi Das; Ameya Godbole; Dilip Kavarthapu; Zhiyu Gong; Abhishek Singhal; Mo Yu; Xiaoxiao Guo; Tian Gao; Hamed Zamani; Manzil Zaheer; Andrew McCallum (MRQA@EMNLP, 2019)