The building had ________ for more than five hours before the fire was put out finally．

1. A.
   caught fire
2. B.
   been on fire
3. C.
   set fire to
4. D.
   set on fire

The building had _____ for more than five hours before the fire was put out finally.

A．caught fire           B．been on fire          C．set fire to            D．set on fire