The correct option is C platelets
Thrombopoiesis is the process of development of thrombocytes. Thrombocytes are also known as platelets. Platelets, along with clotting factors, form blood clot thereby preventing loss of blood from the body.
The process of formation of RBCs is known as erythropoiesis.
The process of formation of WBCs is known as leucopoiesis,
B cells are type of WBCs and hence development of B cells is also known as leucopoiesis.