What is the vehicle that is carrying the ladder?
The vehicle is a trailer.
    src        edge_attr  dst
0     1  to the right of    9
1     1  to the right of    6
2     2   to the left of    7
3     3   to the left of    7
4     4  to the right of   13
5     4  to the right of   10
6     6   to the left of    1
7     7  to the right of    3
8     7  to the right of    2
9     8               on    9
10    9   to the left of    1
11   10   to the left of    4
12   10  to the right of   13
13   13   to the left of   10
14   13   to the left of    4
15   14         carrying    0