13.
A:
Large structures found in ancient civilizations used for astronomical observations.
B:
Microscopic entities containing one or two genes, self-organizing into a rod-like shape, found within the human body.
C:
A type of virus-like entity that replicates independently within the human gut and mouth.
D:
Circular bits of genetic material encapsulated within a protective protein coat, typically found in viroids.
The answer is: B
