Which of the following function prototypes would generate a syntax error?

Question $3$ options:

a$)$

void fun$($int x $=0,$ int y$,$ int z $=0)$;

b$)$

void fun$($int x $=0,$ int y $=0,$ int z $=0)$;

c$)$

void fun$($int$,$ int, int$)$;

d$)$

void fun$($int x$,$ int y$,$ int z$)$;