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");}