Erythropoietin is an hormone and in the bone marrow it helps in the synthesis or in the production of the red blood cells, also Erythropoietin can be used as medication in form of epogen to fight anemia is mainly produced by the kidney.
Increase or rise in the level of Erythropoietin is as a result of low oxygen level which may cause anemia. Also, the higher the altitude one go, the lower the oxygen level. Also, option 'a' that is the disruption in the flow of blood to the kidney also increase Erythropoietin levels.