Biology help?

Because A and G have two closed rings while T and C have only 1. If it is of uniform length, A would have to pair up with T or C and G would have to pair with the other. This meant that A could not pair with G and C could not pair with T. We then used hydrogen base pairing to show that A and T have two hydrogen bond areas while C and G have three, making A and T perfect partners to bond with each other and the same for C and G.