若有定义:float w;int a,b;则合法的switch语句是
A.
switch (w) { case 1.0:printf ("*\n"); case 2.0:printf ("**\n"); }
B.
switch (a) ; { case 1.0:printf ("*\n"); case 2.0:printf ("**\n"); }
C.
switch (b) { case 1:printf(“*\n); default:printf(“\n”); case a:printf(“**\n”); }
D.
switch (a + b); { case 1:printf ("*\n"); case 2:printf ("**\n") ; default:printf ("\n") ; }