Consider the bushy tree shown in the picture. If we are going to join five tables A, B, C, D, E as in the order of the tree shown in the figure, and we specify that D, E must be siblings, how many possible ways do we have to fit A, B, C, D, E into the given tree and join them? Assume that the order of siblings does not matter. For example, assigning D to R1 and E to R is considered as the same as assigning D to R5 and E to R1 R3 R2 R4 R1 R5 (a) 6 (b) 24 (e) 12 (d) 5