A shoping mall is running a scheme: Each packet of detergent SURF contains a coupon which bears letter of the word SURF, if a person buys at least four packets of detergent SURF, and produce all the letters of the word SURF, then he gets one free packet of detergent.
If a person buys 8 such packets at a time, then the number of different combinations of coupon he has is
A. `4^(8)`
B. `8^(4)`
C. `.^(11)C_(3)`
D. `.^(12)C_(4)`