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( {case 1.0: printf("*\n"); case 2.0: printf("**\n");}
B．switch((in; { case 1: printf("*\n"); case 2: printf("**\n");}
C．switch(a + { case 1: printf("*\n"); case 2+1: printf("**\n");}
D．switch(a+ { case 1: printf("*\n"); case c: printf("**\n");}