若有定义: float w; int a,b; 则合法的switch语句是
A. switch(a) { case1: printf("*\n"); case 2: printf("**\n"); }
B. switch(w) { case 1: printf("*\n"); case 2: print("**\n"); }
C. switch(b) { case 1: printf("*\n"); default: printf("\n"); case 1+2: printf("**\n"); }
D. switch(b) { case1: printf("*\n"); case 2: printf("**\n") default:printf("\n") }