Problem: study the following diagram, and state whether or not it is possible (USING ONLY 4 STRAIGHT LINES) to draw a line through every circle without taking your pen/pencil off the paper.

O O O

O O O

O O O

If you think it is possible, explain how it could be done (I E which route should be taken). We will label the circles as follows:

A B C

D E F

G H I