The correct option is D Spleen
Spleen is one of the most important organ of the body. Here are few of its functions
1) In fetal and some part of the neonatal period the spleen works not only as the storehouse of red blood cells or RBCs , but also is one of the important organ for hematopoiesis I.e., the formation of new RBCs.
2) It also acts as a storehouse of various types of white blood cells or WBCs which are used to fight against various infections like pneumococcus, meningococcus etc.
3) It is also known as graveyard of RBC as old and damaged RBC are destroyed in spleen.