Consider, two ideal diatomic gases A and B at some temperature T. Molecules of the gas A are rigid, and have a mass m. Molecules of the gas B have an additional vibrations mode, and have a mass `m/4`. The ratio of the specific heats (`C_(V)^(A)` and `C_(V)^(B)`) of gas A and B, respectively is:
A. `7:9`
B. `3:5`
C. `5:9`
D. `5:7`
