The correct option is C Monocytes
Leucocytes are also known as white blood cells (WBC) as they are colourless due to the lack of haemoglobin. There are two main categories of WBCs - granulocytes and agranulocytes. Neutrophils, eosinophils and basophils are different types of granulocytes, while lymphocytes and monocytes are the agranulocytes. Monocytes are the largest type of corpuscles in human.