Which kind of vehicle is black?
The vehicle is a train.
    src        edge_attr  dst
0     2  to the right of    6
1     3               on   10
2     4   to the left of   17
3     4   to the left of   13
4     6  to the right of   17
5     6  to the right of   12
6     6   to the left of    2
7     6  to the right of   13
8     7   to the left of   11
9     8   to the left of   11
10   11  to the right of    7
11   11   to the left of   14
12   11  to the right of    8
13   12   to the left of    6
14   13  to the right of    4
15   13   to the left of    6
16   14  to the right of   15
17   14   to the left of   19
18   14  to the right of   11
19   15   to the left of   14
20   17   to the left of    6
21   17  to the right of    4
22   19  to the right of   14