尝试编译投影仪时出现以下错误：未定义的控制序列。\begin{document}

Question

代码如下：

\documentclass[hyperref={pdfpagelabels=false}]{beamer}

\mode<presentation>
\usetheme{Berlin}
\setbeamercovered{transparent}

\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{times}
\usepackage[T1]{fontenc}
\usepackage{xcolor}


\subject{Talks}


%\beamerdefaultoverlayspecification{<+->}
\title{Hadronization of a Fourth-Generation Top Quark
    and measurement of its Lifetime}

\author[]{sss }
\date{\today}

%\begin{document}
\begin{document}    
    \frame{\titlepage}
    
    \begin{frame}{Plan of My Talk}
        \begin{itemize}
            \item Motivation for an extra generation of quark.
            \item Electroweak constraint on fourth generation.
            \item Lifetime and branching ratios of $t'$ quark.
            \item Measurement of \textcolor{violet}{$\Gamma_{t'}$} and \textcolor{violet}{$V_{t'b'}$}.
            
        \end{itemize}
    \end{frame}
\end{document}