\item \self SAT solvers usually require input formulas to be in
    \emph{Conjunctive Normal Form} (CNF). In the following list, tick
    all items that conform to CNF.

\begin{itemize}
  \item[$\square$] A formula $\phi$ that consists of a conjunction of clauses $c_1, c_2, \ldots, c_n$.
  \item[$\square$] A formula $\phi$ that consists of a disjunction of clauses $c_1, c_2, \ldots, c_n$.
  \item[$\square$] A formula $\phi$ that consists of a conjunction of cubes $c_1, c_2, \ldots, c_n$.
  \item[$\square$] A formula $\phi$ that consists of a disjunction of cubes $c_1, c_2, \ldots, c_n$.
  \item[$\square$] A literal $l$.
\end{itemize}