A unit rate is a rate in which A-one of the quantities is
B-the quantities add up to
C-both of the quantities are 1
D-neither of the quantities is 1.

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:

to this answer it would be edge enhancement

answerclassical conditioning;