3. Three samples of the same idcal gas (the ratio of heat capacitiesγ = 1.5) have equal volumes and temperatures. The volume of each sample is doubled, the process being isothermal, adiabatic, and isobaric, respectively. If the final pressures are equal for the three samples, the ratio of their initial pressure is (A) 1:1:1, (B) 2:2:1, (C) 1:2:1, (D) (E)