20）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((int)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) {case1:printf(**\n);} casec:printf(**\n);}