Greta starts using a new baking technique, and she can now do twice as much of everything. In a single day, Greta can now make 10 cakes or 8 pies, rather than the 5 cakes and 4 pies she could previously bake. Greta's production possibility frontier has_______, and her opportunity cost of making pies O a. not changed; has increased b. not changed; has decreased c. shifted right; has decreased O d. shifted right; is unchanged