\documentclass[fleqn,11pt]{article}
\usepackage{amsmath}
\setlength{\mathindent}{0.1in} %equations intended by one inch
\setlength{\jot}{.2in} %increases space b/w lines of eqnarray by .2in

\newtheorem{theorem}{\bf Theorem}
\newtheorem{proposition}[theorem]{\bf Proposition}
\newtheorem{lemma}[theorem]{\bf Lemma}
\newtheorem{corollary}[theorem]{\bf Corollary}
\newtheorem{definition}[theorem]{\bf Definition}


\newtheorem{example}[theorem]{\bf Example }

% the proofs and counterexamples

\newenvironment{proof}%
    {\par \noindent {\bf Proof:}}%
    {\par \indent}
\newenvironment{counterexample}%
    {\par \noindent {\bf Counterexample:}}%
    {\par \indent}

% the remarks

\newenvironment{remark}%
    {\par \noindent {\bf Remark: }}%
    {\par \indent}

% abbreviations of existing commands

\newcommand{\be}{\begin{equation}}
\newcommand{\bes}{\begin{displaymath}}
\newcommand{\ee}{\end{equation}}
\newcommand{\ees}{\end{displaymath}}
\newcommand{\ra}{\rightarrow}
\newcommand{\Var}{\mbox{Var}}

% frequently used text pieces and formulas

\newcommand{\rap}{\stackrel{P}{\rightarrow}}
\newcommand{\raL}{\stackrel{\mathcal{L}}{\longrightarrow}}
\newcommand{\deq}{\stackrel{d}{=}}

% other customized commands

\newcommand{\mathbold}[1]{\mbox{\boldmath $\bf#1$}}
\newcommand{\bin}[2]{%
\renewcommand{\arraystretch}{.5} \left({\setlength{\arraycolsep}{0mm}
\begin{array}{c} #1 \\ #2 \end{array}} \right)
\renewcommand{\arraystretch}{1} }
\newcommand{\gdots}{\cdot \ldots \cdot}

\usepackage{latexsym}% necessary for end of proof symbol according to
                     % Jim

%\usepackage{rotate,epsfig}% necessary for figures

\setlength{\textwidth}{15cm} %\setlength{\topmargin}{-.2in}
%\setlength{\headsep}{0in}
%\setlength{\headheight}{0in}
\setlength{\textheight}{21cm} \setlength{\oddsidemargin}{0.7 cm}
\setlength{\evensidemargin}{0.7cm}
\renewcommand{\baselinestretch}{1.2}
%***********************************************

\begin{document}

\section{ section 1}

In  \ref{appendix A}, we have

in  \ref{Appendix B} , we have 

In \ref{Appendix C}, we have
\section*{References}
\begin{description}

\begin{appendix}
\section{sample 1}\label{Appendix B}
sample 1
\end{appendix}


\begin{appendix}
\section{sample 2}\label{Appendix B}
sample 2
\end{appendix}

\begin{appendix}
\section{sample3}\label{Appendix B}
sample 3
\end{appendix}
 \end{document}