What vehicle is made of metal?
The vehicle is a train.
    src        edge_attr  dst
0     0   to the left of   14
1     2   to the left of   12
2     2   to the left of   15
3     4             near   12
4     5  to the right of    6
5     6   to the left of    5
6     7   to the left of   16
7     7  to the right of    8
8     8   to the left of   16
9     8   to the left of    7
10   10   to the left of   14
11   12             near    4
12   12          next to    4
13   12  to the right of    2
14   13               on   10
15   14  to the right of   10
16   14  to the right of    0
17   15  to the right of    2
18   16  to the right of    7
19   16  to the right of    8