Why Was the Coding Region of the Gene for Human

Why was the coding region of the gene for human antithrombin placed near the regulatory region of a gene that is only expressed in the goat's mammary cells?

A) This ensured that the protein would be produced at high levels in all cells.
B) This ensured that the protein would appear in the milk.
C) This ensured that the two proteins would combine into a larger protein.
D) Both genes produce commercially desirable proteins.
E) Only mammary cells actually produce protein.