Based on the pedigree diagram, which two people must be heterozygous for the trait?
A. The mother and son
B. The father and mother
C. The son and daughter
D. The father and daughter

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

i think the answer is gold im not entirely sure

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.