Acknowledgments
This work was supported by grants from the National Natural Science Foundation of China (Nos. 82070912, 81773326, and 81471095), the Key Project of Research and Development of Ningxia Hui Autonomous Region of China (No. 2017BN04), a grant from the Natural Science Foundation of Jiangsu Province China (No. BK20171347 and BE2019676) and the Qing Lan Project of Jiangsu Province China. We thank Prof Erguang Li for his critical review and thoughtful discussion of the manuscript.