What is the fence near the truck made of?
The fence is made of metal.
    src        edge_attr  dst
0     0            below    6
1     0   to the left of   11
2     1           inside    6
3     1   to the left of    4
4     2  on the front of    6
5     3  to the right of   10
6     3   to the left of    9
7     3   to the left of    8
8     3   on the side of    6
9     4           behind    7
10    4             near    5
11    4  to the right of    6
12    4  to the right of    1
13    4          next to    5
14    5            below    6
15    5             near    4
16    5             near   10
17    6             near    7
18    6               on    5
19    6            above    0
20    6  to the right of   10
21    6   to the left of    4
22    7          next to    6
23    7      in front of    4
24    7             near    6
25    8  to the right of    3
26    9  to the right of    3
27   10   to the left of    3
28   10             near    5
29   10   to the left of    6
30   11  to the right of    0