$($a$)$ Draw a graph of the reference variables showing the links between the two classes when the following code fragment is executed. The two lines of code create an instance of the Lens class and then an instance of the Camera class using the lens $1$ as one of its arguments.

Lens I $=$ new Lens $(16)$;

Camera c $=$ new Camera$($I$,$"Canon", "EOS $850$D$")$