$2$ Runtime Environment $(7$ Points$)$

$```$

int alpha$($int a$)\{$

if$($a

return beta$($a$+2,$a$+1)-2$;

return gamma$($a $-1)$;

$\}$

int beta$($int b$,$ int c$)\{$

$\}$

return c $-$ b;

int gamma$($int d$)\{$

if $($d

return $1$;

return alpha$($d $-1)*$ alpha$($d $-2)$;

$\}$

int delta$($int e$)\{$

if $($e$<mn>3</mn><mi>)</mi>$

return beta$($e$,$ e $+2)+2$;

return gamma$($e $-3)$;

$\}$

int main$()\{$

int result $=4$;

printf$("$Result: $\%$d

$",$ gamma$($result$))$;

return $0$;

$\}$

$```$

$1.$ Draw the activation tree generated by executing the above code where the function main is the entry point. $[4$ Points$]$