Take an open ring. You can either anchor it to something, or you can treat it as your source ring.
Before you close the ring, slip a 2x2 unit on to it. Now close the ring.
Take a second open ring, and slip it in place parallel to the first open (but now closed) ring. Make sure it goes through exactly the same rings that the first open ring went through, but that the first open ring does not cross the new open ring.
Call the pair of open (but now closed) rings "pair A."
The next pair of rings will be "pair B" and the outer most rings are "pair C."