Lungs have a pulmonary circulation
Answer: mucilaginous sheath
Explanation:
Quite sure C is correct ;) remember that humans are also placental mammals.
Pork and beef insulins are similar to human insulin, differing only in one or a few amino acids. However, even a slight difference is enough to elicit an allergic response in some people. To overcome this problem, researchers looked for ways to make insulin that would more closely resemble human insulin.