One of the Challenges Associated with the Successful Use of Chemotherapy

Multiple Choice

 One of the challenges associated with the successful use of chemotherapy for treating brain tumors is the fact that

A) no known chemotherapy agents are effective against the types of tumors that arise in the brain.
B) no chemicals are ever able to pass from the blood supply to the brain.
C) many circulating chemicals are not able to enter the brain.
D) chemicals introduced to the brain do not pass through neural membranes.