\documentclass[12pt]{article}

\usepackage{amsmath,amsthm,amssymb,mathrsfs,lineno}
\begin{document}

Zheng and Lin et al. 
\cite{wenping2007crossing} proved that the crossing number $K_6 \Box P_2$ 
\bibliographystyle{e}
\bibliography{paper.bib}
\end{document}
	