If the work done on the system or by the system· is zero, which one of the following statements for a gas kept at a certain volume is correct?

• A. Change in internal energy of the system is equal to flow of heat in or out of the system.
• B. Change in internal energy of the system is less than heat transferred.
• C. Change in internal energy of the system is more than the heat flow.
• D. Cannot be determined.