What is the vehicle that the car is behind of called?
The vehicle is a train.
    src        edge_attr  dst
0     0  to the right of    6
1     0   to the left of    8
2     1   to the left of    5
3     1      in front of    3
4     2   to the left of    3
5     2   to the left of    4
6     3   to the left of    5
7     3           behind    1
8     3  to the right of    2
9     4  to the right of    2
10    4               on    3
11    5  to the right of    1
12    5  to the right of    3
13    5  to the right of    9
14    6   to the left of    7
15    6   to the left of    8
16    6   to the left of    0
17    7  to the right of    6
18    8  to the right of    6
19    8  to the right of    0
20    9   to the left of    5