若有定义:float x=1.5;int a=1,b=3,c=2; 则正确的switch语句是（）。

A) switch(x)
case 1.0: printf("*\n");
case 2.0: printf(" * * \n" );
B) switch((iht)x);
case 1: printf(" * \n" );
case 2: printf(" * * \n" );
C) switch(a +b)
case 1: printf(" * \n" );
case 2 + 1: printf(" * * \n" );
D) switch(a + b)
case 1: pfintf(" * \n" );
case c: pfintf(" * * \n");