使用 \usepackage{xeCJK} 时，\textbf 不起作用

Question

\documentclass[10pt]{beamer}
\usetheme[
%%% option passed to the outer theme
%    progressstyle=fixedCircCnt,   % fixedCircCnt, movingCircCnt (moving is deault)
  ]{Feather}










% If you want to change the colors of the various elements in the theme, edit and uncomment the following lines

% Change the bar colors:
%\setbeamercolor{Feather}{fg=red!20,bg=red}

% Change the color of the structural elements:
%\setbeamercolor{structure}{fg=red}

% Change the frame title text color:
%\setbeamercolor{frametitle}{fg=blue}

% Change the normal text color background:
\setbeamercolor{normal text}{fg=black,bg=gray!10}

%-------------------------------------------------------
% INCLUDE PACKAGES
%-------------------------------------------------------
%\usepackage[UTF8]{ctex}
\usepackage{xeCJK}
\setCJKmainfont[BoldFont={华文楷体 Bold}]{楷体} 
%\setCJKsansfont{微软雅黑}
\setCJKmonofont{华文楷体}  

%\setCJKmainfont{华文楷体 Bold}
\setCJKsansfont{华文楷体}

%\setlength{\parindent}{2em}
\renewcommand{\baselinestretch}{1.35}




%\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[T1]{fontenc}
\usepackage{helvet}
\usepackage{multirow}
\usepackage{textcomp}
\usepackage{color}
\usepackage{float}
\usepackage{multicol}
\usepackage[english]{babel}
\usepackage{calc}
\usepackage[absolute,overlay]{textpos}
\usepackage{caption}

\captionsetup{ labelsep=period, font=footnotesize, figurename=图, tablename=表}

%-------------------------------------------------------
% DEFFINING AND REDEFINING COMMANDS
%-------------------------------------------------------

% colored hyperlinks
\newcommand{\chref}[2]{
  \href{#1}{{\usebeamercolor[bg]{Feather}#2}}
}

%-------------------------------------------------------
% INFORMATION IN THE TITLE PAGE
%-------------------------------------------------------

\title[] % [] is optional - is placed on the bottom of the sidebar on every slide
{ % is placed on the title page
      \textbf{title}
}

\subtitle[institute]
{
    %  \textbf{v. 1.0.0}
}

\author[ author]
{        \\
      {\ttfamily  }
}

 \institute[]
 {


  %there must be an empty line above this line - otherwise some unwanted space is added between the university and the country (I do not know why;( )
 }

%\date{\today}
\date{2017.4.21}
%-------------------------------------------------------
\begin{document}
\section{测试}
\begin{frame}{测试}


\begin{alertblock}{测试：}

\textbf{加粗} ，不加粗。
\end{alertblock}



\end{frame}
%-------------------------------------------------------



{\1
\begin{frame}[plain,noframenumbering]
  \finalpage{谢谢 ！}
\end{frame}}

\end{document}