If you also encouter this latex error: Undefined control sequence. <recently read> \multirow , i think this tutorial will help you.
How does this error occur?
The main reason is missing package:multirow
To solve this error, you should use \usepackage{multirow}
Here is an example:
\documentclass[preprint,12pt]{elsarticle}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{float}
\usepackage{multirow}
\usepackage{graphicx}
\journal{Knowledge-Based Systems}
\begin{document}
\begin{frontmatter}