The blood-brain barrier occurs when the physical structures of the brain prevent blood from intermingling with the extracellular fluid of brain cells. this separation makes it difficult and dangerous to deliver drugs to specific regions of the brain. therefore, further research on how the blood-brain barrier works is needed to allow more effective delivery of drugs. what potential ethical issues may inhibit such research?

The embryos of a bird, a reptile, and a mammal are similar in appearance. how does comparing the physical appearance of embryos of different species support the theory of evolution? a. it shows that these organisms share a common ancestor. b. it provides evidence that these organisms eat the same foods.c. it shows that these organisms share the same habitat.d. it provides evidence that these organisms suffered a genetic mutation.