the concentration of proteins synthesized in the breast is more affected by the

The correct question for this is: "The concentration of proteins synthesized in the breast are more affected by than ."

The correct answers are the age of the infant and maternal intake and maternal serum proteins. 

While maternal intake and serum proteins contribute to the proteins synthesized in the breast tissue, the age of the infant will affect the composition of the breast milk as he or she ages. This is because of the reason that the demand for nutrients of the infant should be fulfilled until the recommended breastfeeding age of 2 years old.