Ingested Protein Is Always Degraded to Amino Acids Before Absorption

Ingested protein is always degraded to amino acids before absorption in the mature human small intestine, but nursing infants can absorb intact antibodies (large protein molecules) from breast milk. How might this difference in intestinal function be explained?

A) The tight junctions that prevent molecules from creeping through the epithelial lining of the small intestine are not yet fully developed in infants.
B) The anchoring junctions that interlock adjacent cells can be selectively activated or disabled in infants to permit the selective passage of specific substances.
C) Infants have gap junctions that open to the lumen of the small intestine and admit appropriately sized proteins.
D) Any of the above is a reasonable explanation.