\begin{frame}[t]
  \frametitle{Exercise}
  
  \structureAll
  \medskip

  \begin{quiz}{0.95\textwidth}{Formulate the following query in SQL}
    The topics of all exercises solved by George Orwell?
  \end{quiz}
  \pause\bigskip

  We need tuple variables for \sql{Students} and \sql{Exercises}.
  \begin{tcenter}
  \begin{code}{\textwidth}{}
    \small
    \BUseVerbatim{query}
  \end{code}
  \end{tcenter}  
  \pause\medskip
  
  \begin{alertblock}{}
  \emph{Problem}: \sql{S} and \sql{E} are \emph{unconnected}!
  \end{alertblock}
\end{frame}