The city of Robville is divided into five suburbs labelled as `A` to `E` on the map below.
A lake which is situated in the city is shaded on the map.
A table is constructed to represent the number of land borders between suburbs.
If there is no land border between two suburbs, the table records a '0'. If there is a single land border between two suburbs, the table records a '1', and if there are two separate land borders between the same two suburbs, the table records a '2'.
- Explain why all values in the final row and final column of the table are zero. (1 mark)
In the network diagram below, vertices represent suburbs and edges represent land borders between suburbs.
The diagram has been started but is not finished.
- The network diagram is missing one edge and one vertex.
On the diagram
- draw the missing edge (1 mark)
- draw and label the missing vertex. (1 mark)