A. YES B. NO C. YESNO D. 语句错误
A. if(x>0) y=1; else if(x<0) y=-1; else y=0; B. if(x)if(x>0)y=1; else if(x<0) y=-1; C. y=-1;if(x)if(x>0)y=1; else if(x==0) y=0; else y=-1; D. y=0; if(x>=0) if(x>0) y=1; else y=-1;