Ans: D
Note that the distance between $A$ and the line $x=1$ is $4$. Note also that the distance between the object and the reflectional axis is equal to the distance between the image and the reflectional axis. Therefore, the distance between $A$ and $B$ is $8$.
Note that the distance between $A$ and the line $x=1$ is $4$. Note also that the distance between the object and the reflectional axis is equal to the distance between the image and the reflectional axis. Therefore, the distance between $A$ and $B$ is $8$.
