\documentclass[a4paper]{article}

\usepackage{longtable}
\usepackage{probsoln}

 %\showanswers

\newcounter{problem}
\renewcommand{\PSNitem}{\refstepcounter{problem}%
\theproblem. }
\renewcommand{\endPSNitem}{\\}

\renewenvironment{solution}{}{}

\newcommand{\selected}{\fbox{$\times$}}
\newcommand{\notselected}{\fbox{\phantom{$\times$}}}

\begin{document}
\begin{longtable}{lrrrl}
\bfseries Question & \bfseries A & \bfseries B & 
\bfseries C & \ifshowanswers \bfseries Reason\fi\\
\selectrandomly{tabmchoice}{2}
\end{longtable}
\end{document}
