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
如图,在四边形ABCD中,AD∥BC,F在CD上,且AF垂直平分CD,FG平分∠AFD,交AD于G,连接GB,交AF于N,且FN=FD.
表
一
实验序号
1
2
3
4
5
6
7
8
9
密度ρ(g/cm3)
2.0
2.5
3.0
重力G (N)
12
压力F (N)
4.0
6.0
2.4
4.8
7.2
二
(ρ﹣ρ水):ρ
1:2
3:5
2:3
F:G