Limb bones within unrelated animals that have the same basic structures are considered

a. homologous structures.
b. analogous structures.
c. embryological.
d. vestigial structures.

Limb bones within unrelated animals that have the same basic structures are considered homologous structures. Homologous structures are similar structures shared by unrelated species. An example is that birds and humans have the similar anatomy of limb bones, however, these are two unrelated groups of animals that share similar structures. Therefore, this is the example of  A. homologous structures.
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The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass

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