Among 4 persons A, B, C and D. A takes twice as much time as B to complete a piece of work. B takes twice as much time as C and C takes twice as much time as D to complete the same work. One group of three of the four men can complete the work in 11 days while another group of three can do so in 7 days. Which is the group that takes 11 days? a) A.B.C b) A,B,D c) B,C,D d) None of the above