B - They have repeating steps
Explanation:
I'm guessing the answer is oxygen.
Answer: adult tissues
Explanation: Adult stem cells. These stem cells are found in small numbers in most adult tissues, such as bone marrow or fat. Compared with embryonic stem cells, adult stem cells have a more limited ability to give rise to various cells of the body.
The cleanliness of a ecosystem or how healthy it is. It determines how clean an environment/ecosystem is. You need all types of animals living there, therefore making it more healthy. The more healthy, the more we can say that it is biodiverse.
