Which of the following statements about red blood cells is false?

a. They live about 120 days before being replaced.

b. They lack a nucleus and other organelles when they are mature.

c. They are replaced when the hormone EPO stimulates stem cells in bone marrow.

d. They are replaced as part of a negative feedback loop in which kidney cells monitor blood oxygen levels.

e. All the above statements are true except b, because all cells require a nucleus in order to function properly.