Selectively permeable means that cells only allow certain molecules to enter or exit a cell.
Thymine and cytosine are classified as "Pyrimidines" and have one ring of carbon and nitrogen atoms for each base.
I think the correct answer from the choices listed above is option A. Horned toads squirt blood from their eyes as a means of evading predators. This is their final defense action which frightens their predators. Hope this answers the question. Have a nice day.
