9. The pressure of an ideal gas becomes three times of its initial pressure during an adiabatic process. What is the ratio of its final volume to its initial volume? γ is the ratio of the constant-pressure specific heat to the constant-volume specific heat of this.
(A) 1/3
(B) 3-γ
(C) 3γ
(D) 3-1/γ
(E) 31/γ