How to create a Title Answer using exam package?

Question

I've been a user of this place for a long time and searched several solutions about typing latex correctly.

I've tried to write a simple exam paper and similar to this @Phil Hirschorn's answer like this and this. I have problems with making 2 columns using the mcq tests.

I really like making a simple exam to look like this:

and when I use \showallanswers we print this header

Any suggestion?

\documentclass[11pt,a4paper,twocolumn]{exam}
\usepackage{amsmath,amsthm,amsfonts,amssymb,dsfont}
\usepackage{ifthen}
\usepackage{multicol}


% Accumulate the answers. Unmodified from Phil Hirschorn's answer
% Showing Solutions of the Questions "separately"
\newbox\allanswers
\setbox\allanswers=\vbox{}

\newenvironment{answer}
{%
    \global\setbox\allanswers=\vbox\bgroup
    \unvbox\allanswers
}%
{%
    \bigbreak
    \egroup
}

\newcommand{\showallanswers}{\par\unvbox\allanswers}
% End Phil's answer

% Is there a better way?
\newcommand*{\getanswer}5{%
    \ifthenelse{\equal{#5}{a}}
    {\begin{answer}\thequestion. (a)~#1\end{answer}}
    {\ifthenelse{\equal{#5}{b}}
        {\begin{answer}\thequestion. (b)~#2\end{answer}}
        {\ifthenelse{\equal{#5}{c}}
            {\begin{answer}\thequestion. (c)~#3\end{answer}}
            {\ifthenelse{\equal{#5}{d}}
                {\begin{answer}\thequestion. (d)~#4\end{answer}}
                {\begin{answer}\textbf{\thequestion. (#5)~Invalid answer choice.}\end{answer}}}}}
}

\setlength\parindent{0pt}
%usage \choice{ }{ }{ }{ }
%(A)(B)(C)(D)
\newcommand{\fourch}5{
    \par
    \begin{tabular}{*{4}{@{}p{0.23\textwidth}}}
        (a)~#1 & (b)~#2 & (c)~#3 & (d)~#4
    \end{tabular}
    \getanswer{#1}{#2}{#3}{#4}{#5}
}

%(A)(B)
%(C)(D)
\newcommand{\twoch}5{
    \par
    \begin{tabular}{{2}{@{}p{0.46\textwidth}}}
        (a)~#1 & (b)~#2
    \end{tabular}
    \par
    \begin{tabular}{{2}{@{}p{0.46\textwidth}}}
        (c)~#3 & (d)~#4
    \end{tabular}
    \getanswer{#1}{#2}{#3}{#4}{#5}
}

%(A)
%(B)
%(C)
%(D)
\newcommand{\onech}5{
    \par
    (a)~#1 \par (b)~#2 \par (c)~#3 \par (d)~#4
    \getanswer{#1}{#2}{#3}{#4}{#5}
}

\newlength\widthcha
\newlength\widthchb
\newlength\widthchc
\newlength\widthchd
\newlength\widthch
\newlength\tabmaxwidth

\setlength\tabmaxwidth{0.96\textwidth}
\newlength\fourthtabwidth
\setlength\fourthtabwidth{0.25\textwidth}
\newlength\halftabwidth
\setlength\halftabwidth{0.5\textwidth}

\newcommand{\choice}5{%
\settowidth\widthcha{AM.#1}\setlength{\widthch}{\widthcha}%
\settowidth\widthchb{BM.#2}%
\ifdim\widthch<\widthchb\relax\setlength{\widthch}{\widthchb}\fi%
    \settowidth\widthchb{CM.#3}%
\ifdim\widthch<\widthchb\relax\setlength{\widthch}{\widthchb}\fi%
    \settowidth\widthchb{DM.#4}%
\ifdim\widthch<\widthchb\relax\setlength{\widthch}{\widthchb}\fi%

% These if statements were bypassing the \onech option.
% \ifdim\widthch<\fourthtabwidth
%     \fourch{#1}{#2}{#3}{#4}{#5}
% \else\ifdim\widthch<\halftabwidth
% \ifdim\widthch>\fourthtabwidth
%     \twoch{#1}{#2}{#3}{#4}{#5}
% \else
%      \onech{#1}{#2}{#3}{#4}{#5}
%  \fi\fi\fi}

% Allows for the \onech option.
\ifdim\widthch>\halftabwidth
    \onech{#1}{#2}{#3}{#4}{#5}
\else\ifdim\widthch<\halftabwidth
\ifdim\widthch>\fourthtabwidth
    \twoch{#1}{#2}{#3}{#4}{#5}
\else
    \fourch{#1}{#2}{#3}{#4}{#5}
\fi\fi\fi}

\begin{document}

\Large

\noindent{\bf Ma 12 Long Test 1\hfill 9 February 2017}

\medskip\hrule

\begin{questions}

\question Um capacitor $C$ é submetido a uma tensão $V$. A energia armazenada no capacitor é igual a: 
\choice{$CV^2$}{$0.5CV^2$}{$2CV^2$}{$CV$}{b}

\question Uma tensão V é aplicada a um circuito RL em série. A corrente em regime permanente é igual a: 
\choice{$V/R$}{$V/L$}{$\dfrac{V}{\sqrt{R^2+L^2}}$}{zero}{a}

\question If the amplitude of a complex number is $\dfrac{\pi}{2}$ then the number is
\choice{purely imaginary}{purely real}{0}{neither real nor imaginary}{a}

\question The value of $i + i^{22} + i^{23} + i^{24} + i^{25}$ is
\choice{i}{-i}{1}{-1}{c}

\question The volume generated by rotating the triangle with vertices at (0, 0), (3, 0) and (3, 3) about x-axis is
\choice{$18\pi$}{$2\pi$}{$36\pi$}{$9\pi$}{a}

\question To complete the song, the last answer should be
\choice{a}{b}{c}{d}{e} % Invalid answer choice


\question To complete the song, the last answer should be 
\choice{a long tex a long tex a long tex a long tex a long tex a long tex a long tex a long tex a long tex}{b}{c}{d}{a} 
\end{questions}

%\newpage  %Uncomment to put on new age
\bigskip
Answer Key:
\bigskip  
\showallanswers % Phil Hirschorn
\end{document}

Answer 1

As stated in the comments, it seems that you want to do two things: create a two columns environment and then add the horizontal line in the answer section.

For creating two (or more columns), you can use the multicol package. A possible way of using it would be:

% more preamble
\usepackage{multicol}

\begin{document}

\begin{multicols}{3}  % the number here is the number of columns
[  % the part between square brackets isn't divided into columns
\section{First Section}
All human things are subject to decay. And when fate summons, Monarchs must 
obey.
]  % now the columns start
Hello, here is some text without a meaning.  This text should show what 
a printed text will look like at this place.
If you read this text, you will get no information.  Really?  Is there 
no information?  Is there...
\end{multicols}

% rest of the document

Using the previous code with the exam package options, you can create several columns with your code.

For creating the horizontal rule without the number in the name of the section, you can use the following code:

\section*{Answer to Practice Exercises}
\hline

Or you can use \rule if you have problems with interline spacing:

\section*{Answer to Practice Exercises}
\rule{\textwidth}{0.4pt}

This last part should be inside the \showallanswers (which, by the way, is a command from the exam package?)