请问各位大佬，如何修改局部的字体以及字号呢？

\documentclass[UTF8]{ctexart} \usepackage{hyperref} \usepackage{graphicx} \usepackage{perpage} %the perpage package \MakePerPage{footnote} %the perpage package command \usepackage[a4paper,left=25mm,right=25mm,top=15mm,bottom=12mm]{geometry} \usepackage{color} \usepackage{tabularx} \usepackage{amssymb} \usepackage{amsmath} \setCJKfamilyfont{lmm}{lmmono10-regular.otf} \newcommand{\lmm}{\CJKfamily{lmm}} \setCJKfamilyfont{song}{simsun.ttc} \newcommand{\song}{\CJKfamily{song}} \setCJKfamilyfont{xh}{STXIHEI.TTF} \newcommand{\xh}{\CJKfamily{xh}} \setCJKfamilyfont{kt}{STKAITI.TTF} \newcommand{\kt}{\CJKfamily{kt}} \setCJKfamilyfont{ht}{simhei.ttf} \newcommand{\simhi}{\CJKfamily{ht}} \newcommand{\chuhao}{\fontsize{42pt}{\baselineskip}\selectfont} \newcommand{\xiaochuhao}{\fontsize{36pt}{\baselineskip}\selectfont} \newcommand{\yihao}{\fontsize{28pt}{\baselineskip}\selectfont} \newcommand{\erhao}{\fontsize{21pt}{\baselineskip}\selectfont} \newcommand{\xiaoerhao}{\fontsize{18pt}{\baselineskip}\selectfont} \newcommand{\sanhao}{\fontsize{15.75pt}{\baselineskip}\selectfont} \newcommand{\sihao}{\fontsize{14pt}{\baselineskip}\selectfont} \newcommand{\xiaosihao}{\fontsize{12pt}{\baselineskip}\selectfont} \newcommand{\wuhao}{\fontsize{10.5pt}{\baselineskip}\selectfont} \newcommand{\xiaowuhao}{\fontsize{9pt}{\baselineskip}\selectfont} \newcommand{\liuhao}{\fontsize{7.875pt}{\baselineskip}\selectfont} \newcommand{\qihao}{\fontsize{5.25pt}{\baselineskip}\selectfont} \linespread{1.5} \usepackage{hyperref} \usepackage{fancyhdr} \renewcommand{\headrule}{} \headrule \pagestyle{fancy} \lfoot{} \newcommand{\tabincell}[2]{\begin{tabular}{@{}#1@{}}#2\end{tabular}} \begin{document} \kt \xiaosihao $\bullet$1.如图 S$_{1}$、S$_{2}$是两个相干光源，它们到P点的距离r$_{1}$和r$_{2}$。路径S$_{1}$P垂直穿过一块厚度为t$_{1}$ ，折射率为n$_{1}$的介质板，路径S$_{2}$P垂直穿过厚度为t$_{2}$，折射率为n$_{2}$的另一介质板，其余部分可看作真空，这两条路径的光程差等于\qquad $\left[\quad \right]$\\ A$\centerdot$\quad (r$_{2}$+n$_{2}$t$_{2}$)\ -\ (r$_{1}$+n$_{1}$t$_{1}$)\\ B$\centerdot$\quad (r$_{2}$+(n$_{2}$-1)t$_{2}$)\ -\ (r$_{1}$+(n$_{1}$-1)t$_{1}$)\\ C$\centerdot$\quad (r$_{2}$-n$_{2}$t$_{2}$)\ -\ (r$_{1}$-n$_{1}$t$_{1}$)\\ D$\centerdot$\quad n$_{2}$t$_{2}$\ -\ n$_{1}$t$_{1}$\\ \end{document}

麻烦你用代码块。 一般，我们会这么用 ```tex { \FZSS 这里写内容 } ``` 从你的代码里没有见到这样的用法似的。