分别运行下列两段程序后，y1和y2的值是______。
程序段1：
#define f(x) x*x
float x, y1;
x=2.0;
y1=x/f(x);
程序段2:
#define f(x) (x*x)
float x, y2;
x=2.0;
y2=x/f(x);

A．virtual private network
B．local area network
C．storage area network
D．WLAN