This will give you Vector{Tuple{Int64, Int64, Int64}} →
[(i, j, D[idx]) for (idx, i) in enumerate(B) for j in C[idx] if (i, j) in A]
This will give you Vector{Tuple{Int64, Int64, Int64}} →
[(i, j, D[idx]) for (idx, i) in enumerate(B) for j in C[idx] if (i, j) in A]