can somebody explain?

13) Draw all four of the constitutional isomers of C3H6Cl2 below: ( 10 pts.) \begin{tabular}{|c|c|c|c|} \hline Isomer 1 & Isomer 2 & Isomer 3 & Isomer 4 \\ \hline & & & \\ \hline Cl2HCH2CH3 & ClH2CCCCH3 & H3CCl2CH3 & ClH2CC2CH2Cl \\ \hline \end{tabular}