The authors would like to thank the referee for the valuable suggestions and comments. L.Z. Ruan would like to express heartfelt thanks to Professor Zhouping Xin for his valuable discussions on this topics during he visited at IMS, The Chinese University of Hong Kong. The research of L.Z. Ruan was supported in part by the Natural Science Foundation of China #11771169, #11331005, Program for Changjiang Scholars and Innovative Research Team in University #IRT17R46, and the Special Fund for Basic Scientific Research of Central Colleges #CCNU16A02011. The research of Wei Xiang was supported in part by the Research Grants Council of the HKSAR, China (Project No. CityU 21305215, Project No. CityU 11332916, and Project CityU 11304817). The research of Lili Fan was supported in part by the Fundamental Research Grants from the Science Foundation of Hubei Province under the contract 2018CFB693.