Answer:
the only building block is a two-input, four output decoder (with an active highe enable). the truth table is shown:
EN A B 0 1 2 3
0 X X 0 0 0 0
1 0 0 1 0 0 0
1 0 1 0 1 0 0
1 1 0 0 0 1 0
1 1 1 0 0 0 1
A------ --------0
B------ --------1
--------2
--------3
Explanation: