What determines the similarities in anatomical features among organisms?

The most common example that determines the similarities in anatomical features among organisms is the bone structure, commonly used in comparative anatomy. For example, the forelimbs or appendages of bats, humans, cats and whales have the same basic parts but they differ in function. Fins of whales and wings of bats have the same skeletal parts, but fin is used for swimming while wing is for flight. These structures could be termed as homologous, analogous, or homoplastic. However, recent developments have been made than just basing to the skeleton - the main reason why we have comparative genomics today. 

Carbon dioxide is the correct answer