Which of the following is an illegal method declaration?

a$.$ private static void CreateStatement$($int acctNum $=0,$ double balance$)$

b$.$ All of these are legal.

c$.$ private static void CreateStatement$($int acctNum, double balance $=0\mathrm{.}0)$

d$.$ private static void CreateStatement$($int acctNum $=0,$ double balance $=0)$