Ice floats on a lake. This characteristic of water is responsible for -

A: suffocation of aquatic organisms
B: mixing a lake's thermal layers
C: altering migration patterns of fish
D: preventing a lake from freezing solid

Option D) preventing a lake from freezing solid

Explanation:

This is based on the difference in density of water in solid form as against it's liquid form

Ice, which is water in solid form is less dense to water as liquid water. Hence, ice floats on liquid water, thereby preventing the total freezing of the lake which would lead to death of aquatic organisms living in polar regions

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.