%% Question, Exercise, Solution
\usepackage{theorem}
\theoremstyle{break} 
\newtheorem{Ext}{Exercise}
\newtheorem{Question}{Question}

\newenvironment{Exercise}{
  \renewcommand{\labelenumi}{\alph{enumi}.}\begin{Ext}%
}{\end{Ext}}
\newenvironment{Solution}{%
  \noindent\textbf{Solution:}\renewcommand{\labelenumi}{\alph{enumi}.}%
}{\bigskip}
