This question is from my module theory assignment and I am struck on this particular problem.
Prove that if D is a ring with identity such that every D-module is free, then D is a divison ring.
Attempt: To prove that D is Divison Ring it is sufficient to show that D has no proper ideals. Let on the contrary D has a proper ideal I. Now , I have to somehow prove that some D-module is not free. But I am not able to get any ideas.
Can you please help?