75. In diabetes treatment, the long-acting insulin glargine can provide stable basal insulin levels. Compared to native human insulin, what changes were made to its amino acid sequence that reduce its solubility at subcutaneous physiological pH to form microprecipitates, thereby prolonging its duration of action? (A) The last three amino acids of the B chain were removed. (B) Asparagine (Asn) at position 21 of the A chain is replaced with glycine (Gly), and two arginines (Arg) are added to the C-terminus of the B chain. (C) The proline (Pro) at position 28 and the lysine (Lys) at position 29 of the B chain were swapped. (D) The linkage positions of the disulfide bonds were altered to hide the receptor-binding region.