\documentclass[a4paper]{article}

\usepackage{probsoln}

% Sample file illustrating use of \selectallproblems
% All problems defined in specified file will be used
% in order of definition

\showanswers

\begin{document}
Differentiate the following functions:
\begin{enumerate}
\selectallproblems{easy}
\end{enumerate}
\end{document}
