有一个分段函数，当x大于0时，y的值是1；当x为0时，y的值是0；当x

A、if(x > 0) y = 1;else if(x == 0) y = 0；else y = -1;
B、y = 0;if(x > 0) y = 1;else if(x

C、y = 0;
if(x >= 0); if(x > 0) y = 1; else y = -1;
D、if(x >= 0)if(x > 0) y = 1;else y = 0;else y = -1;