定义变量float x;int a,b；
则正确的switch语句是(  )
A switch(x)                              B switch(x)

{case 1.0:printf("*\n");                     {case 1,2:printf("*\n");
case 2.0:printf("**\n");                      case 3:printf("**\n");
}                                             }


C switch(x)                              D switch(x)
                                              {case 1:printf("*\n");
{case 1:printf("*\n");                          case 1+2:printf("**\n");
case 2*a:printf("**\n");                       }
}