1. The correct answer is d. Vitamin B₁₂ is absorbed in the ileum and requires intrinsic factor manufactured by parietal cells in the stomach for absorption. Excess amounts are stored in the liver.

2. The correct answer is c. New, not fully matured RBCs are called reticulocytes. They are produced in the bone marrow and sent into circulation. Their amount indicates how fast or slow the bone marrow is making new RBCs and is a first indicator that therapy for iron deficiency anemia is working.

3. The correct answer is b. People with chronic illnesses, in addition to the underlying chronic condition itself, often suffer from the problems listed, making it difficult for them to take in and use sufficient iron to meet body requirements.

4. The correct answer is b. This is a heterozygous situation; with only one gene passed on, the child has the trait and will be essentially asymptomatic.

5. The correct answer is d. Pernicious anemia is an autoimmune disease in which the individual can no longer absorb vitamin B₁₂ from the gut and needs to have it supplemented monthly for life.

6. The correct answer is c. Those with thalassemia minor experience a persistent mild anemia that they compensate for with increased RBC production. The other choices are all sequelae of thalassemia major, which is a severe, life-threatening disorder.