Question: Point out the correct answer regarding the regulation of hematopoiesis: 
 Options:  <1> Altitude inhibits hematopoiesis. <2> Erythropoietin inhibits hematopoiesis. <3> Hypoxia stimulates the production of erythropoietin. <4> Erythropoietin is synthesized in the liver. <5> Erythropoietin does not influence the production of red blood cells.
3