RG PA at SemEval-2021 Task 1: A Contextual Attention-based Model with RoBERTa for Lexical Complexity Prediction. - Gang Rao; Maochang Li; Xiaolong Hou; Lian-Xin Jiang; Yang Mo; Jianping Shen (SemEval@ACL/IJCNLP, 2021)