#### Answer

If there is an edge which connects two vertices, then the two vertices are said to be adjacent.
Even though two vertices are close together on a graph, they are not necessarily adjacent. If there is no edge which connects two vertices, then the two vertices are not adjacent.

#### Work Step by Step

It is quite simple to determine if two vertices are adjacent.
If there is an edge which connects two vertices, then the two vertices are said to be adjacent.
Even though two vertices are close together on a graph, they are not necessarily adjacent. If there is no edge which connects two vertices, then the two vertices are not adjacent.