有一个函数关系如下所示:x0 时,y=x-1x=0 时,y=xx0 时,y=x+1下面程序段中,能够正确表示上面关系的是（）。

A.y = x + 1if x >= 0:if x == 0:y =xelse:y = x - 1;

B.y = x - 1if x != 0:if x > 0:y = x + 1else:y = x

C.if x <=0:if x< 0:y = x - 1else;y = xelse:y = x + 1

D.y = xif x <=0:if x < 0:y = x - 1else:y = x + 1

正确答案：if x <=0:if x< 0:y = x - 1else;y = xelse:y = x + 1