<｜begin▁of▁sentence｜>### Instruction:
As an ergonomist, you've been tasked with evaluating the design and layout of a network diagram visualization tool used in an office environment. Using the function AbstractCairoVertexDrawer.draw, you'll need to create a visual representation of a network graph with 3 nodes, and output the result into a PDF file named 'graph_vertex_draw.pdf'. This will allow you to assess the visual clarity and ergonomic aspects of the graph representation for the end users.
### Response:
import igraph as ig
from igraph.drawing import plot

# Create a simple igraph graph with 3 vertices
g = ig.Graph.Erdos_Renyi(n=3, p=0.5)

# Set up Cairo drawing backend
visual_style = {'vertex_size': 20}
drawer = ig.drawing.Plot(
    target='./graph_vertex_draw.pdf',
    bbox=(300, 300),
    **visual_style
).cairo

# Draw the vertices using the AbstractCairoVertexDrawer
drawer.set_vertex_drawer(ig.drawing.vertex.AbstractCairoVertexDrawer)
for vertex in g.vs:
    drawer.draw_vertex(vertex)

drawer.finish()
<|EOT|>
