Answer:
A. These homologous structures indicate that these four organisms all share a common ancestor.
Explanation:
Homologous structures mean the organs will have similar structure, but not necessarily function (human arm vs whale's flipper). While analogous structures are similar in function but not structure (wings of an airplane vs wings of a bird). Since the question states that they are similar in skeletal structure, we know they must be homologous structures, thereby eliminating B and C. D is not a choice because the question does not provide anything about the order of evolution. Therefore the answer is A. These homologous structures indicate that these four organisms all share a common ancestor.
This contributes because their lifestyle revolves around food, and if they live near different areas, they will have to search for different types of food.
Bursa - A small sac that lubricates the area around a joint where friction is most likely to occur
ex. elbow, knee, or shoulder
Anaerobic respiration (without oxygen) would caused muscle cells to produce lactic acid. This causes the muscles to ache and in the long term, damages them. Also anaerobic respiration releases far less energy (ATP) than aerobic respiration. So it is best for muscle cells to respire aerobically as they need more energy.
