A small box x contains 7 cookies, and a large box y contains 15 cookies. Andrew bought 12 boxes of cookies containing a combined total of 120 cookies.
Select all the equations that correctly describe the cookie purchase.
A. x+y=15
B. x+y=12
C. x+y=120
D. 7x+15y=120
E. 15x+7y=120
F. 8x+12y=120