\begin{enumerate}
\item Write down the additional terms $H_{kin}'$ of the kinetic part
of the Hamiltonian.
- \item Chose a reasonable vector potential ${\bf A}$ to get a constant
+ \item Choose a reasonable vector potential ${\bf A}$ to get a constant
magnetic field ${\bf B}$ in $z$-direction.
\item Rewrite the Hamiltonian
using the definition of the angular momentum operator