Why would 131I be used to specifically destroy the thyroid gland and have minimal effect on other cells And tissues in the body

Aclient with pernicious anemia asks why she must take vitamin b12 injections for the rest of her life. what is the nurse's best response? a. "the reason for your vitamin deficiency is an inability to absorb the vitamin because the stomach is not producing sutficient acid." b. "the reason for your vitamin deficiency is an inability to absorb the vitamin because the stomach is not producing sufficient intrinsic factor." c. "the reason for your vitamin deficiency is an excessive excretion of the vitamin because of kidney dysfunction." d. "the reason for your vitamin deficiency is an increased requirement for the vitamin because of rapid red blood cell production."