有如下程序：
#include ＜iostream＞
using namespace std;
class Demo
public:

Demo () cout ＜＜ "default constructor\n";
Demo (const Demo &x) cout ＜＜ "copy constructor\";
;
Demo userCode(Demo b) Demo c(b);return c;
int main()

Demo a,d;
cout＜＜"calling userCode()\n";
d=aserCode(

A．;
ret

UPS电源“Bypass”灯亮表示UPS处于什么状态？