Which of the following statements is true about the movement of fluid in a convection cell? A Cool fluid rises because it is less dense.
B. Hot fluid rises because it is denser.
C. Cool fluid sinks because it is denser.
D. Hot fluid sinks because it is less dense.

Explanation:

C. Cool fluid sinks because it is denser.

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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.

c. heat from the poles back down towards the equator.