John waited at the bus-stop for nearly half an hour           the bus finally arrived .

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

John waited at the bus-stop for nearly half an hour           the bus finally arrived .

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

 John waited at the bus-stop for nearly half an hour _____ the bus finally arrived .

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

 John waited at the bus-stop for nearly half an hour _____ the bus finally arrived .

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

John waited at the bus-stop for nearly half an hour           the bus finally arrived .

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