The correct option is D Monocyte
Platelets are the blood cells, whose function is to stop bleeding.
Eosinophils are a type of WBCs. They are granulocytes and are involved in combating infections by releasing granule proteins or by degranulation.
Basophils are granulocytes i.e., they contain large cytoplasmic granules in the cell nucleus and store histamine (a vasodilator).
Monocytes are a type of WBCs which along with their macrophages serve three main functions as phagocytosis, antigen presentation and cytokine production.
Thus, the correct answer is option D.