A family member is caring for a client diagnosed with Alzheimer's disease. Which of the following is most likely to cause the caregiver depression and role strain ？（）
A．The caregiver had a close relationship with the client before diagnosis of the illness.
B．The caregiver has no formal support, such as a visiting nurse or day care worker.
C．The caregiver understands the full reality of the disease and its inevitable progression.
D．The caregiver feels unable to control the client and unable to cope with caregiving.