The answer is going to be the letter D, nitrogen. I hope this helps!!
Answer: B
Explanation: Researchers have induced differentiating cells to revert to being stem cells. According to Spradling, it has long been known that some specialized, or differentiated, cells in the body can revert to become stem cells to regenerate tissue under particular conditions
We can limit fishing and hunting to certain seasons. This allows the population to increase and continue breeding, but we still get food. We can limit cutting down trees so that ecosystems can survive. Many species have lost homes due to deforestation. By cutting down only some trees in an area, we can still have wood to use, and we can save ecosystems.
The letter I is just there. Blood type problems will usually have

and

= blood type A

and

= blood type B

would be blood type AB
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would be blood type O.
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So the answer would be B since B is the only option that the offspring would be only blood type B, which is the same as their parents.