The chairman was about to declare the conference open ____ the lights went all out.

           A. as                       B. while                      C. then                        D. when

The chairman was about to declare the conference open ____ the lights went all out.

1. A.
   as
2. B.
   while
3. C.
   then
4. D.
   when

The chairman was about to declare the conference open ____ the lights went all out.

         A. as                 B. while                C. then                  D. when

The chairman was about to declare the conference open ____ the lights went all out.

A．as           B．while            C．then           D．when

The chairman was about to declare the conference open ____ the lights went all out.