引起缺铁性贫血的最常见原因是：（）

A.铁的摄入不足

B.铁的吸收不良

C.慢性失血

D.铁的需要量增加

E.骨髓造血功能不良

—Do you know that Jack（）a postman for about six years
—Yes, I see.

A. has become

B. has turned

C. has changed

D. has been