49. B. $\text{C}_6\text{H}_{12}\text{O}_6 \to 2\text{C}_3\text{H}_4\text{O}_3 + 4\text{H} + 2\text{ATP}$ Glycolysis is the metabolic pathway that breaks down one molecule of glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) into two molecules of pyruvate ($\text{C}_3\text{H}_4\text{O}_3$). In this process, a net of 2 ATP molecules are produced, and 2 $\text{NAD}^+$ molecules are reduced to 2 NADH (represented as 4H, indicating the transfer of electrons and protons). 50. D. Any blood group A patient with blood group AB is known as the universal recipient. This is because their red blood cells have both A and B antigens, and their plasma does not contain anti-A or anti-B antibodies. Therefore, they can safely receive blood from donors of any ABO blood group (A, B, AB, or O) without an immune reaction.