The blood-brain barrier
a. is fully developed in humans when they are born.
b. prevents many drugs from entering the brain.
c. is designed to allow all drug compounds into the brain.
d. cannot be penetrated, even with trauma to the brain.

The correct option is B.
The blood brain barrier is designed to prevent the passage of some substances such as drugs from the blood stream into the brain. The blood brain barrier is made up of high density cell barriers which restrict passage of substances into the brain area.