$3.$ Consider the following definitions:

function main$()\{$

var x$,$ y$,$ z;

function A$()\{$

var a$,$ y$,$ z;

function B$()\{$

var a$,$ b$,$ z;

$...$

$\}$

$...$

$\}$

$...$

$\}$

The referencing environment of a statement is the collection of all names $($variables$)$ that are visible in the statement. Assuming static scoping rules. What is the referencing environment in the body of function B$?$