下面的程序段执行后,变量a,b,c的值分别为? 
int a,b,c; 
a=(int)Math.round(-4.51); 
b=(int)Math.ceil(-4.51); 
c=(int)Math.floor(-4.51);
A -5,-4,-5
B -4,-4,-5
C -5,-5,-5
D -4,-4,-4