During Treatment of a Patient Who Has Brain Cancer, the Nurse

During treatment of a patient who has brain cancer, the nurse hears the oncologist mention that the patient has reached the "nadir." The nurse knows that this term means which of these?

A) The lowest level of neutrophils reached during therapy.
B) The highest level of neutrophils reached during therapy.
C) The point at which the adverse effects of chemotherapy will stop.
D) The point at which the cytotoxic action against cancer cells is the highest.