What is the gray sidewalk made of?
The sidewalk is made of concrete.
    src        edge_attr  dst
0     1   to the left of    5
1     1   to the left of   10
2     1   to the left of    2
3     2  to the right of    1
4     2  to the right of    8
5     5  to the right of    8
6     5   to the left of   10
7     5  to the right of    1
8     7   to the left of    9
9     8   to the left of    2
10    8   to the left of   10
11    8   to the left of    5
12    9  to the right of   14
13    9  to the right of    7
14   10  to the right of    1
15   10  to the right of    5
16   10  to the right of    8
17   12          wearing   13
18   14   to the left of    9