Which of the following is NOT an effective way for the astronauts to treat the ailments th

Which of the following is NOT an effective way for the astronauts to treat the ailments they have？

A．To eat vitamin D to strengthen the bones.

B．To have some blood let out to reduce iron.

C．To take exercises to relieve the back pain.

D．To have folate acid to improve the vision.

请帮忙给出正确答案和分析，谢谢！