Let the efficiencies of A and B be 4a and 5b respectively. Since C is 25 percent less efficient than A, the efficiency of C is 3a. Since D is 20 percent more efficient than B, the efficiency of D is 6b. We are given that A and B together take 12 days, so their combined rate is 1/12, meaning 4a plus 5b equals 1/12. We are also given that C and D together take 12 days, so 3a plus 6b equals 1/12. Multiplying the first equation by 3 and the second by 4 gives 12a plus 15b equals 1/4 and 12a plus 24b equals 1/3. Subtracting the first from the second gives 9b equals 1/12, so b equals 1/108. Substituting b back into the second equation gives 3a plus 6/108 equals 1/12, which means 3a equals 3/108, so a equals 1/108. The combined efficiency of A, B, and C is 4a plus 5b plus 3a, which equals 7a plus 5b. Substituting the values gives 7/108 plus 5/108, equaling 12/108 or 1/9 of the work per day. Therefore, they will complete the work in 9 days. The correct answer is 9.