有以下程序 #include ＜stdio.h＞ struct tt { int x; struct tt *y; } *p; struct tt a[4]= {20,a+ 1,15,a+2,30,a+3,17,a}; main() { int i;p=a;for(i=1; i＜-2; i++) { printf("%d,", p-＞x ); p=p-＞y; }

A．20,30,

B．30,17

C．15,30,

D．20,15,

ZXA10 F820直流电源板的接线端子分别为（）.

A.+48V

B.-48V

C.-48地

D.PE