Homologous traits are found in two or more species because . a. those traits are from a common ancestor. b. Both of the other answers are correct. c. some evolutionary process (usually natural selection) has independently fashioned similar traits in each species.

The correct answer is a. those traits are from a common ancestor.

Explanation:

Homologous structures are the structure that may be superficially different or may do not share the same function but they are developmentally related to each other because homologous structures are derived from a common ancestor.  

For example, wings of bats and forelimbs of birds are homologous structures which means they share a common ancestor. Divergent evolution is responsible for producing homologous structures. In divergent evolution, related species become more dissimilar. Therefore the correct answer is a.

b. the carbon cycle ensures living things have a source of hydrogen

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.