Genetic engineering is the direct manipulation of a specific gene. I would use it in this scenario
To study the Blood-Brain Barrier requires that research involves the use of subjects such as guinea pigs, rabbits, or even humans. The research would involve conducting different treatments with different substances to check which their movement or effect on this barrier. The research may also involve opening up or severing of the brain for analysis. This, will, therefore, raise ethical issues on the use of human subjects, and the respect for human dignity and bodily integrity. The research would have to comply with the ethical rule of non‐maleficence which may limit the frontiers of the research hence limit its success.
Lemons contain more citric acid.
So if there's a lot of oxygen outside of the cell, and there's only a little bit less oxygen inside the cell, diffusion occurs slowly. If there's lots more oxygen outside of the cell than inside, oxygen moves into the cell more quickly. So saying that I believe it would be cell A because it has the most oxygen outside and the least inside.