\newproblem{
%\FPsetpar{a}{2}{5}
\estrai[2]{2,3,7}{a}
\item \PTs{1} exercise 1a $a=\ai$
  \begin{answers}{1}\bChoices[random]
    \Ans1 answer 1 correct\eAns
    \Ans0 answer 2 wrong\eAns
    \Ans0 answer 3 wrong\eAns
    \eChoices\end{answers}}

\newproblem{
\FPsetpar{a}{2}{5}
\item \PTs{1} exercise 1b $a=\a$
  \begin{answers}{1}\bChoices[random]
    \Ans1 answer 1 correct\eAns
    \Ans0 answer 2 wrong\eAns
    \Ans0 answer 3 wrong\eAns
    \eChoices\end{answers}}