#### Answer

Vertex C, vertex E, and vertex F are adjacent to vertex D.

#### Work Step by Step

Two vertices are adjacent if there is an edge which connects the two vertices.
There is an edge which connects vertex D and vertex C, so vertex C is adjacent to vertex D.
There is an edge which connects vertex D and vertex E, so vertex E is adjacent to vertex D.
There is an edge which connects vertex D and vertex F, so vertex F is adjacent to vertex D.
Vertex C, vertex E, and vertex F are adjacent to vertex D.