\documentclass[12pt]{article}
\usepackage{amsmath,amssymb,amsfonts}
\begin{document}
In this paper, we deal with zero-divisor graphs of posets. We prove that
the diameter of such a graph is either 1, 2 or 3 while its girth is either
3, 4 or $\infty$. We also characterize zero-divisor graphs of posets in
terms of their diameter and girth.
\end{document}