\begin{exercice}
  \'Ecrire le plus simplement possible. 
  \begin{colenumerate}{2}
   \item $\vv{MB}-\vv{MD}$
   \item $\vv{CB}-\vv{CD}-\vv{BD}$
   \item $\vv{BD}-\vv{BA}+\vv{MA}-\vv{MD}$
   \item $\vv{BD}-\vv{MC}-\vv{BM}+\vv{DB}$
   \item $\vv{MA}+\vv{EM}-\vv{CA}-\vv{EC}$
   \item $-\vv{AU}+\vv{SH}-\vv{ST}+\vv{MU}$
  \end{colenumerate}
 \end{exercice}
