Consider the following skeletal $C$ program: $[25$ points$]$

void fun$1($void$)$; $/*$ prototype $*/$

void fun$2($void$)$; $/*$ prototype $*/$

void fun$3($void$)$; $/*$ prototype $*/$

void main$()\{$

int $a,b,c$;

$\}$

void fun$1($void$)\{$

int b$,$ c$,$ d;

$\}$

void fun$2($void$)\{$

int $c,d,e$;

$\}$

void fun$3($void$)\{$

int $d,e,f$;

$\}$

Given the following calling sequences and assuming that dynamic scoping is used, what

variables are visible during execution of the last function called? Include with each

visible variable the name of the function in which it was defined.

a$.$ main calls fun$1$; fun$1$ calls fun$2$; fun$2$ calls fun$3.$

b$.$ main calls fun$1$; fun$1$ calls fun$3.$

c$.$ main calls fun$2$; fun$2$ calls fun$3$; fun $3$ calls fun$1$

d$.$ main calls fun$3$; fun$3$ calls fun$1.$