1. limb bones within unrelated animals that have the same basic structures are considered
a. vestigial structures.
b. homologous structures.
c. analogous structures.
d. embryological.

B.
The Radio-ulna and digits of most primates and animals represents a homologous structure

An example of another internal structure is the genes.
The homologous chromosomes have the same genes in common. Each cell has at least two sets of chromosomes which one comes from one’s father also called as paternal chromosome and mother, called as the maternal chromosomes. These chromosomes are what makes the child obtain the characters and may depend on the traits the parents possess. Homologous chromosomes are not duplicated chromosomes or identical however, they are analogous or similar. The alleles for a specific characteristics isn’t the same but the same genes are in the same order. 

They both determine the exact age of rocks.