A:Seeing a boy lying on the road
B:On seeing a boy sitting on the road
C:The minute the driver saw a boy seated on the road
D:The driver had seen a boy standing on the road
小清喜欢跟妈妈一起下厨,她发现厨房的菜刀磨得很锋利,这是为了在压力一定时,减小受力面积, ____ 压强;她还认为如图所示油壶的壶嘴和壶身组成了一个 ____ .