2points
why do only active margins have trenches?
o
a. trenches are filled with basalt.
o
b. trenches are caused by subduction.
o
c. only passive margins have subduction.
o
d. trenches are caused by erosion.

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.