The correct option is D GP
Let α,β,γ the roots of x3−14x2+56x−64=0
α+β+γ=14αβ+βγ+γα=56αβγ=64
Now let roots are in G.P, such that αγ=β2
αβγ=64⇒β3=64⇒β=4⇒αγ=16
And αβ+βγ+γα=β(α+γ)+16=β(14−β)+16=4(10)+6=56
Therefore, roots are in GP
Hence, option 'D' is correct.