若有定义:float x=1.5;
A. switch(a+b){ case 1: printf("*\n");case 2+1: printf("**\n"); }
B. switch((int)x);{ case 1: printf("*\n");case 2: printf("**\n"); }
C. switch(x){ case 1.0: printf("*\n");case 2.0: printf("**\n"); }
D. switch(a+b){ case 1: printf("*\n");case c: printf("**\n"); }