[Song, Yiping;Mou, Lili;Yan, Rui;Zhang, Ming] Peking Univ, Beijing, Peoples R China.^[Mou, Lili] Peking Univ, MoE, Key Lab High Confidence Software Technol, Beijing, Peoples R China.^[Yan, Rui] Baidu Inc, Nat Language Proc Dept, Beijing, Peoples R China.^[Yan, Rui;Yi, Li;Zhu, Zinan;Hu, Xiaohua] Cent China Normal Univ, Sch Comp, Wuhan, Hubei, Peoples R China.