18. The constant-volume specific heat C_V (heat capacity per mole) for a diatomic ideal gas is shown in the following figure. Which of the following statements is correct?

(A) Electronic excitations can be largely triggered at 2000K
(B) Vibrational motion ceases at 50K
(C) Vibrational excitations can be largely triggered at 300K
(D) Rotational motion can be rarely found at 50K
(E) All of the above statements are correct.