若a、b、c1、c2、x、y、均是整型变量,正确的switch语句是().
A. switch(a +b);{ case 1:y =a +b;break;case 0:y =a -b;break;}
B. switch(a +b){ case 3:case 1:y =a +b;break;case 3:y =b -a,break; }
C. switch a{ case c1:y =a -b;break;case c2:x =a *b;break;default: x =a +b; }
D. switch(a -b){ default:y =a *b;break;case 3:case 4:x=a +b;break;case 10:case 11:y =a -b;break; }