问题
选择题
______, 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
答案
答案：C
考查状语从句，句意：这名司机看到一个男孩站在在公路上，因此他立刻停下来。这是一个原因状语从句，后面已经有了so，前一个分句不能出现because，所以选C。