Which material is the sidewalk made of?
The sidewalk is made of concrete.
    src        edge_attr  dst
0     0               by   20
1     0             near   13
2     1   to the left of   11
3     3   to the left of   12
4     3            below    9
5     3            below   10
6     4   to the left of    8
7     4  to the right of   16
8     4   to the left of    7
9     5           beside    0
10    6   to the left of   12
11    7  to the right of    4
12    7  to the right of   16
13    7  to the right of   17
14    8  to the right of    4
15    8  to the right of   16
16    8  to the right of   17
17    9            above    3
18   10  to the right of   17
19   10            above    3
20   10  to the right of   14
21   10  to the right of   16
22   11  to the right of    1
23   12  to the right of    6
24   12  to the right of    3
25   13          next to    0
26   14   to the left of   18
27   14   to the left of   10
28   14   to the left of   16
29   16  to the right of   21
30   16  to the right of   14
31   16   to the left of   10
32   16   to the left of   18
33   16   to the left of    4
34   16   to the left of    8
35   16   to the left of    7
36   17   to the left of    7
37   17   to the left of    8
38   17   to the left of   10
39   17   to the left of   18
40   18  to the right of   17
41   18  to the right of   16
42   18  to the right of   14
43   21  to the right of   22
44   21   to the left of   16
45   22   to the left of   21