\documentclass{article}
\usepackage{latex-macros/course}

\begin{document}
\decideaboutsolutions

Sample file for using problems.

\begin{problem}
A

\solution{a}
\end{problem}


\begin{problem}
B

\solution{b}
\end{problem}


\begin{problem}
C

\solution{a}
\end{problem}


\begin{problem*}
D

\solution{d}
\end{problem*}

\end{document}