Why is Secretory IgA (sIgA) found in colostrum and mucosal secretions highly resistant to proteolytic degradation in the harsh environment of the infant's gastrointestinal tract?

Options:

• A: Because it exists as a monomer with highly hydrophobic variable regions.
• B: Due to the presence of the secretory component wrapped around the IgA dimer, which sterically hinders enzymatic cleavage.
• C: Because it contains a high concentration of disulfide bonds in its heavy chain constant region (CH3).
• D: Due to its association with maternal macrophages that shield it from gastric acid.

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