Your friend says he had stored a semisoft cheese (blue cheese) in his refrigerator for three weeks. He asks you why the outer "skin" of the cheese is so much thicker than it was when he originally purchased the cheese. You tell him that

A) Fungal enzymes have made more curd.
B) Fungi have been growing.
C) Fungal enzymes have digested the curd.
D) Lactic acid bacteria have grown on the outside.
E) It dried out.