Which of the following statements are true?I. Each white blood cell contains millions of hemoglobin molecules.II. In a sample of blood, there are more red blood cells than white blood cells.III. HIV destroys red blood cells.IV. All blood cells come from one pool of stem cells.

Statement II is true: red blood cells are far more numerous in blood than white blood cells. Statement IV is also true because the different blood cell types develop from hematopoietic stem cells. Statement I is false because white blood cells do not contain millions of hemoglobin molecules; hemoglobin is found in red blood cells. Statement III is false because HIV primarily attacks certain white blood cells, not red blood cells. Therefore, the true statements are II and IV only, choice A.

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