Understanding the internal structures of X(4140), X(4274), X(4500) and X(4700)Hua-Xing Chen, Er-Liang Cui, Wei Chen, Xiang Liu and Shi-Lin ZhuEur. Phys. J. C, 77 3 (2017) 160DOI: https://doi.org/10.1140/epjc/s10052-017-4737-5