Actually you are all underthinking this. Read the question properly. It says "used in" not FINAL PRODUCT. It is true the final product can be any of them, but the one that is "used" is D.
Please remember that the more important part of the question was how a comparative study increases the appreciation of both texts. The ambition part everyone would of had.
2012 School Rank: 8 (Sydney Boys High) (Though last year was a bad year)
My subject ranks:
English: 7
Chemistry: 8
Physics: 11
Mathematics Extension 2: 35
Mathematics Extension 1: 35