What is the output of the following code:

int fun$($int $x=0,$ int $y=5,$ int $z)$

$\{$

return $(x+y+z)$;

$\}$

int main$()$

$\{$

cout $$ fun$(10)$;

return $0$ ;

$\}$

Select one:

a$.5$

b$.10$

C$.15$

d$.$ error