分数空间

Question

查看与分数线的距离...我怎样才能降低一点 \partial W？

\documentclass[10pt,a4paper]{letter}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\begin{document}
\[\frac{\partial W}{\partial t}\]
\end{document}