Thymine and cytosine are classified as "Pyrimidines" and have one ring of carbon and nitrogen atoms for each base.
It is A. Those are all decomposers, the other answers like C are all animals. Decomposers are are biotic organisms that break down basically dead plants or animals.
Answer(s):
Box One= A Gene
Box Two= A Chromosome
Box Three= Heredity
I hope this helps! If it is wrong, I am very sorry! ;-;
