One of the Main Differences Between PPOs and HMOs Is

One of the main differences between PPOs and HMOs is that

A) HMO physicians charge on a traditional fee-for-service basis, while PPO physicians do not.
B) HMOs are usually for-profit organizations, whereas PPOs are not.
C) PPOs employ their own doctors, whereas HMOs do not.
D) PPO physicians charge on a traditional fee-for-service basis, while HMOs do not.