Time taken by A to complete a work=4 days
Time taken by B to complete a work=8 days
Time taken by C to complete a work=16 days
Time taken by D to complete a work=32 days
Time taken by pair (A,D) to complete a work=4 + 32=-36 days
Time taken by pair (B,C) to complete a work=8 +16 =24 days
(B,C) takes two thirds time Taken by (A,D) to complete the work.
Time taken by (B,C)= $\frac{2}{3}*36=24$
Hence,Option (4)A,D is the Answer.