UKCAT practice question - I'm stuck!?

Question

Here is a print screen of a question I am stuck on,

http://img225.imageshack.us/my.php?image=ukcatpracticeye3.png

The image is meant to belong to set B, but why? What are the rules for each set?

Answer 1

The image belongs to set B.

All of the images in set A have an odd number of (outer) vertices.  All of the images in set B have an even number of (outer) vertices.

Since the image has an even number (8), it belongs to set B

Answer 2

IDK

But it does look like it just belongs in B