How many isomers could be obtained by replacing one hydrogen of propene with chlorine?

Structural isomers have different structures but the same molecular formula. So, the isomers could be obtained by replacing one hydrogen of propene with chlorine are
$$\begin{gathered} {\mathrm{CH}}_2=\mathrm{CH}-{\mathrm{CH}}_3: \\ \mathrm{CHCl}=\mathrm{CH}-{\mathrm{CH}}_3, {\mathrm{CH}}_2=\mathrm{CCl}-{\mathrm{CH}}_3, {\mathrm{CH}}_2=\mathrm{CH}-{\mathrm{CH}}_2\mathrm{Cl} \end{gathered}$$. 
Thus, (C) 3 is the correct answer.