The correct answer is D, white blood cells.
We know that red blood cells deliver nutrients and are not apart of the immune system; platelets are responsible for coagulation, which has nothing to do with the immune system, and plasma is a substance that, again, has nothing to do with immunity. White blood cells are the only things that fight disease (antibodies are white blood cells)!
I hope I helped!
(By nothing I meant very little to none).
All organisms are made of cells
all existing cells are produced by other living cells
the cell is the most basic unit of life
I recall that Professor Kwang had observed amoebas that had cannibalized bacteria cells. The bacteria were slaughtering the amoebas, but somehow some survived. This particular group of amoebas contained bacteria that thrived inside it. Hence the name, endosymbiosis. However, this lucky group and it's offspring could not survive without bacteria.
