7. Which of the following statements is correct? (A) The internal energy of a system increases when more work is done by the system than heat was flowing into the system. (B) The internal energy of a system decreases when work is done on the system and heat is flowing into the system. (C) The system does work on the surroundings when an ideal gas expands against a constant external pressure. (D) All statements are true. (E) All statements are false.