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