______, so he stopped the car at once.

1. A.
   Seeing a boy lying on the road
2. B.
   On seeing a boy sitting on the road
3. C.
   The driver had seen a boy standing on the road
4. D.
   The minute the driver saw a boy seated on the road

______, so he stopped the car at once．

A．Seeing a boy lying on the road

B．On seeing a boy sitting on the road

C．The driver had seen a boy standing on the road

D．The minute the driver saw a boy seated on the road

______, so he stopped the car at once.

A. Seeing a boy lying on the road

B. On seeing a boy sitting on the road

C. The driver had seen a boy standing on the road

D. The minute the driver saw a boy seated on the road